Passive special device for switch terminal on power distribution column

Abstract

The invention provides a passive special device for a switch terminal on a power distribution column, and belongs to the technical field of power systems. Comprising a DC / AC inverter circuit, a photovoltaic charging module, a dual-power switching control circuit, a PWM switching power supply control circuit and a peripheral circuit parameter design, the DC / AC inverter circuit adopts a PWM modulation mode, direct current is converted into alternating current through a full-bridge inverter circuit, and the photovoltaic charging module adopts a photovoltaic floating charging mode to perform balanced charging and discharging on a lithium battery in real time. And the PWM switching power supply control circuit adopts an SG3525A pulse control circuit, and has the functions of an internal reference voltage source, an operational amplifier and under-voltage protection. According to the invention, a photovoltaic charging lithium battery passive self-standby power supply and a voltage transformer secondary power supply are mutually standby dual-power-supply system, so that continuous and reliable power supply of the distribution network line pole-mounted switch terminal is ensured, and the power supply safety and reliability are improved.

Description

Technical Field

[0001] The invention provides a passive special device for switch terminals on distribution poles, belonging to the technical field of power systems. Background Art

[0002] The voltage transformer in PT mode provides power for relay protection devices and distribution automation devices. Since the secondary load capacity of PT is not high, it is easy to cause the transformer to burn out, causing distribution line failure and damage to the pole switch. According to statistics, 75% of the pole switch failures in recent years are caused by the secondary cause of the voltage transformer.

[0003] Based on the above, the inventors found that:

[0004] Traditional switch terminals on distribution poles usually rely on external power supply, which has problems such as unstable power supply and high maintenance cost. With the development of new energy technology, it is possible to use photovoltaic power generation to provide passive power supply for switch terminals on distribution poles. However, the existing passive power supply devices still need to be improved in terms of power conversion efficiency, system stability and lithium battery management.

[0005] Therefore, in view of this, the existing structure is studied and improved, and a passive dedicated device for the switch terminal on the distribution column is proposed to solve the above-mentioned problems. Summary of the invention

[0006] The technical problem to be solved by the present invention is a passive dedicated device for switch terminals on distribution poles, which adopts a dual power supply system in which a passive backup power supply of a photovoltaic-charged lithium battery and a secondary power supply of a voltage transformer serve as backup for each other, ensuring continuous and reliable power supply to the switch terminals on the distribution network line poles and improving power supply safety and reliability.

[0007] In order to solve the above problems, the technical solution proposed in the present invention is: a passive special device for switch terminals on distribution poles, including a DC / AC inverter circuit, a photovoltaic charging module, a dual power supply switching control circuit, a PWM switch power supply control circuit, and peripheral circuit parameter design. The DC / AC inverter circuit adopts PWM modulation to convert direct current into alternating current through a full-bridge inverter circuit. The photovoltaic charging module adopts a photovoltaic floating charge mode to balance the charging and discharging of lithium batteries in real time to improve the endurance of lithium batteries. The PWM switch power supply control circuit adopts an SG3525A pulse control circuit with an internal reference voltage source, an operational amplifier and undervoltage protection functions.

[0008] Furthermore, the DC / AC inverter circuit switch tube is selected as MUR460, the operating frequency is 20kHz, to ensure that the harmonic content of the output voltage is low, and the output filter inductor and capacitor are selected as 5.5mH and 5μF / 250VAC respectively to filter out high-order harmonics and ensure the THD requirements of the output voltage.

[0009] Furthermore, the photovoltaic charging module needs to work in conjunction with the inverter circuit to ensure that the system can still operate stably without an external power supply.

[0010] Furthermore, the dual power supply switching control circuit is based on the dual power supply backup principle, and adopts a passive power supply and a voltage transformer secondary dual power supply backup mode. The main power supply is a passive power supply, and the backup power supply is a voltage transformer secondary power supply. When the main power supply fails or fails, the backup power supply automatically takes over the power supply to achieve continuous and stable operation of the system.

[0011] Furthermore, the PWM switching power supply control circuit adopts the SG3525A pulse control circuit, which has an internal reference voltage source, an operational amplifier and undervoltage protection functions. By adjusting the duty cycle of the output pulse, the output voltage is stabilized at about 300V. When the circuit is abnormal, the control pin is turned off to stop working in time to protect the subsequent output circuit and the switching power MOS tube.

[0012] Furthermore, the operating frequency of the peripheral circuit parameter design is set at 60kHz, which is achieved by setting the parameters of CT=0.001μF, RT=22kΩ, and RD=470Ω.

[0013] Due to the adoption of the above technical solution, the beneficial effects of the passive dedicated device for switch terminals on distribution poles of the present invention are as follows:

[0014] 1. Provide passive backup power for the switch terminals on the distribution network line poles, and balance the charging and discharging of lithium batteries through photovoltaic charging mode to improve the endurance of lithium batteries. Adopting inverter rectification technology, the 24V lithium battery is converted into a sinusoidal AC power supply through inverter boosting, which improves the reliability and safety of the power supply of the switch terminals on the distribution network line poles, avoids the use of the voltage transformer secondary power supply mode, and improves the safe and reliable operation of the switch on the distribution network line poles.

[0015] 2. The passive power supply and voltage transformer secondary dual power supply backup system can automatically switch to the backup power supply when one power supply fails or a power outage occurs, ensuring the continuous power supply of the switch terminal on the distribution column. When the main power supply fails, the dual power supply backup system can automatically switch to the backup power supply to ensure the normal operation of the switch terminal on the distribution column. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0017] Figure 1 The present invention is a DC / AC inverter circuit topology diagram of a passive dedicated device for switch terminals on distribution poles.

[0018] Figure 2 This is a switch tube driving waveform diagram of a passive dedicated device for switch terminals on a distribution column of the present invention.

[0019] Figure 3 The present invention discloses an unfiltered bipolar PWM wave diagram of a passive dedicated device for a switch terminal on a distribution column.

[0020] Figure 4 This is the internal logic diagram of SG3525A, a passive dedicated device for switch terminals on distribution poles of the present invention.

[0021] Figure 5 This is the peripheral wiring diagram of SG3525, a passive special device for switch terminals on distribution poles of the present invention. DETAILED DESCRIPTION

[0022] The following will be described clearly and completely in conjunction with the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0023] The present invention provides a passive special device for switch terminals on distribution poles: comprising a passive special device for switch terminals on distribution poles, including a DC / AC inverter circuit, a photovoltaic charging module, a dual power supply switching control circuit, a PWM switch power supply control circuit, and peripheral circuit parameter design. The DC / AC inverter circuit adopts a PWM modulation method to convert direct current into alternating current through a full-bridge inverter circuit. The photovoltaic charging module adopts a photovoltaic floating charge mode to balance the charging and discharging of lithium batteries in real time to improve the endurance of lithium batteries. The PWM switch power supply control circuit adopts an SG3525A pulse control circuit and has an internal reference voltage source, an operational amplifier and undervoltage protection functions.

[0024] The DC / AC inverter circuit switch tube is selected as MUR460, and the operating frequency is 20kHz to ensure that the harmonic content of the output voltage is low. The output filter inductor and capacitor are selected as 5.5mH and 5μF / 250VAC respectively to filter out high-order harmonics and ensure the THD requirements of the output voltage.

[0025] The single-phase bridge inverter circuit in the DC / AC inverter circuit is as follows Figure 1As shown, the operation of the full-bridge inverter circuit requires two sets of drive pulses with opposite phases to control the two pairs of switch tubes M1 and M4 to be turned on and off at the same time, and M2 and M3 to be turned on and off at the same time. The input DC voltage is Vcc, and R represents the load of the inverter; when switches M1 and M4 are turned on, current flows through M1, R and M4, and the voltage polarity on the load is positive at the top and negative at the bottom; when switches M1 and M4 are turned off and M2 and M3 are turned on, current flows through M2, R and M3, and the voltage polarity on the load is reversed, converting DC into AC.

[0026] The photovoltaic charging module needs to work in conjunction with the inverter circuit to ensure that the system can still operate stably without an external power supply.

[0027] The dual power supply switching control circuit is based on the dual power supply backup principle and adopts a passive power supply and a voltage transformer secondary dual power supply backup mode. The main power supply is a passive power supply and the backup power supply is a voltage transformer secondary power supply. When the main power supply fails or fails, the backup power supply automatically takes over the power supply to achieve continuous and stable operation of the system.

[0028] When the main power supply fails or fails, the backup power supply will automatically take over the power supply to achieve continuous and stable operation of the system.

[0029] In the inverter boost dual power switching circuit, the core control device is the PWM switching power supply control circuit. The SG3525A pulse control circuit is used. Compared with the early PWM circuit, the SG3525A circuit has more complete functions, can directly drive the power MOS tube, has an internal reference voltage source, operational amplifier and undervoltage protection function, simple peripheral circuits, and is quite convenient to use. It adopts a 16-pin dual in-line package, and has all the functions of the PWM circuit and a relatively complete support circuit. Its switching frequency is high, and the structure of the output circuit is totem pole type, which can adapt to the new power switch tube, and is convenient for high frequency and miniaturization of the switching power supply.

[0030] The SG352A chip is used in the inverter boost dual power switching circuit. The definition of each pin of the SG3525A circuit Figure 4 shown.

[0031] INVINPUT (inverting input, pin 1): The inverting input of the error amplifier. The gain of the error amplifier is nominally 80dB, and its size is determined by the feedback or output load. The output load can be a pure resistor or a combination of resistor and capacitor components. The common-mode input voltage range of the error amplifier is 1.5V-5.2V. This terminal is usually connected to a resistor divider connected to the power supply output voltage. In negative feedback control, the power supply output voltage is divided and compared with the reference voltage.

[0032] NIINPUT (non-inverting input terminal, pin 2): This terminal is usually connected to the voltage divider resistor of the reference voltage pin 16 to obtain the 2.5V reference comparison voltage and compare it with the sampling voltage of the INVINPUT terminal.

[0033] SYNC (synchronization terminal, pin 3): For external synchronization. When multiple chips need to work synchronously, each chip has its own oscillation frequency, which can be connected to their pins 4 and 3 respectively. At this time, the working frequency of all chips is synchronized with the working frequency of the fastest chip. It is also possible to make a single chip work at an external clock frequency.

[0034] OSCOUTPUT (synchronous output terminal, pin 4): synchronous pulse output. Used when multiple chips work synchronously. However, the operating frequencies of several chips cannot differ too much, and the synchronous pulse frequency should be lower than the oscillation frequency. If multiple chips do not need to work synchronously, pins 3 and 4 are left floating. The output frequency of pin 4 is twice the output pulse frequency. The output sawtooth wave voltage range is 0.6V to 3.5V.

[0035] Ct (oscillation capacitor end, 5-pin): One end of the oscillation capacitor is connected to 5-pin, and the other end is directly connected to the ground. Its value range is 0.001uf to 0.1uF. When working normally, a sawtooth wave varying from 0.6V to 3.5V can be obtained at both ends of Cr.

[0036] Rt (oscillation resistor end, 6-pin): One end of the oscillation resistor is connected to 6-pin, and the other end is directly connected to the ground. The resistance value of Rr determines the internal constant current value to charge Cr. Its value range is 2K to 150K. The larger the Rr and Cr, the longer the charging time, and vice versa.

[0037] DISCHATGERD (discharge end, 7 feet): The discharge of Ct is determined by the dead time resistors at both ends of 5.7. Separating the charging and discharging circuits is beneficial to adjust the dead time through the dead time resistor, making the dead time adjustment range wider. Its value range is 0 to 500. The larger the discharge resistors RD and CT, the longer the discharge time, and vice versa.

[0038] SOFTSTATR (soft start, 8 feet): The inverting end of the comparator is the soft starter control terminal 8, which can be connected to an external soft start capacitor. The capacitor is charged by the internal Vf 50uA constant current source.

[0039] COMPENSATION (Compensation terminal, 9-pin): Connect resistors and capacitors between the error amplifier output terminal 9-pin and the error amplifier inverting input terminal 1-pin to form a PI regulator to compensate for the amplitude-frequency and phase-frequency response characteristics of the system. The operating voltage range of the compensation terminal is 1.5V to 5.2V.

[0040] SHUTDOWN (shutdown terminal, pin 10): Pin 10 is an input terminal of the PWM latch. Generally, an overcurrent detection signal is connected to pin 10. When the overcurrent detection signal is maintained for a long time, the capacitor C connected to the soft start terminal 8 will be discharged. When the circuit is working normally, this terminal is at a high level, and its potential is higher than the peak potential of the sawtooth wave. When the circuit is abnormal, as long as the voltage of pin 10 is greater than 0.7V, the transistor is turned on, and the voltage of the inverting terminal will be lower than the valley voltage of the sawtooth wave, so that the output PWM signal is turned off, which plays a protective role. (Input high-level shutdown signal)

[0041] OUTPUTA, OUTPUTB (pulse output terminal, 11, 14 pins): The output stage adopts a push-pull output circuit, which has a faster shutdown speed when driving a field effect power tube. The phase difference between pins 11 and 14 is 180°, and the current peak reaches 200mA. Due to the existence of opening and closing hysteresis, overlapping conduction occurs between the output and the absorption. There is a current spike pulse at the overlap, which lasts for about 100ns. A capacitor of about 0.luf can be connected to Vc to filter out the voltage spike.

[0042] GROUND (ground terminal, pin 12): All voltages on the chip are relative to GROUND, which is both the power ground and the signal ground. In the experimental circuit, since the feedback voltage connected to the reverse input terminal of the error amplifier is also relative to pin 12, the ground terminals of the main loop and the control loop should be connected.

[0043] VC (push-pull output circuit voltage input terminal, pin 13): As the voltage source of the push-pull output stage, it increases the output power of the output stage. It can share a power supply with pin 15, or use a higher voltage power supply. The voltage range is 18V-34V.

[0044] +VIN (chip power supply terminal, 15-pin): DC power is introduced from 15-pin and divided into two paths, one path is used as the working voltage of the internal logic and analog circuits; the other path is sent to the input of the reference voltage regulator to generate an internal reference voltage of 5.1±1% V. If the voltage of this pin is lower than the threshold voltage (Turnoff: 8V), the internal circuit of the chip is locked and stops working (except for the reference source and necessary circuits) to reduce the current consumption to a very small level (about 2mA). In addition, the maximum voltage of this pin cannot exceed 35V. It should be bypassed directly to the GROUND terminal with a capacitor during use.

[0045] VREF (reference voltage terminal, pin 16): The voltage of the reference voltage terminal pin 16 is internally controlled at 5.1V ± 1%. It can be used as the reference voltage of the error amplifier after voltage division.

[0046] The PWM switching power supply control circuit adopts the SG3525A pulse control circuit, which has an internal reference voltage source, an operational amplifier and an undervoltage protection function. By adjusting the duty cycle of the output pulse, the output voltage is stabilized at about 300V. When the circuit is abnormal, the control pin is turned off to stop working in time to protect the subsequent output circuit and the switching power MOS tube.

[0047] The PWM switching power supply control circuit has an important conclusion in sampling control theory: when narrow pulses with equal impulses but different shapes are added to the inertial link, the effect is basically the same. The impulse refers to the area of ​​the narrow pulse. One cycle of the sine wave is divided into 2N equal parts with equal pulse width, and then the area surrounded by the sine curve and the horizontal axis of each equal part is replaced by a rectangular pulse of equal amplitude and unequal width with the same area, and the midpoint of the rectangular pulse coincides with the midpoint of the corresponding equal part of the sine wave. This series of rectangular pulse waveforms with equal amplitude and unequal width that are equivalent to the sine wave according to the principle of equal area is a sine wave pulse width modulation (PWM) waveform. Unipolar and bipolar sinusoidal pulse width modulation are two basic forms of sinusoidal pulse width modulation.

[0048] DC / AC conversion circuit parameter design

[0049] Switch tube selection

[0050] The voltage stress of the inverter switch tube is Vids = Vdc = 380V

[0051] The effective value of the inverter current is I = P / Vac = 200 / 220 = 0.9A

[0052] The peak current of the switch tube

[0053] The inverter switching frequency fis=20kHz, and MUR460 is selected.

[0054] Vds=500V, Ids=20A, Rds=0.27Ω, Tr=59ns, TON=18ns, Tf=58ns

[0055] Output filter inductor selection

[0056] The reason why the output filter inductor can improve the quality of the output waveform is that the high-order harmonics in the inverter output waveform mainly fall on both ends of the inductor. To ensure that the harmonic content of the output voltage is low, the high-frequency impedance of the filter inductor cannot be too low compared to the filter capacitor, so the inductance value cannot be too small. Increasing the inductance can effectively suppress low-order harmonics, but increasing the inductance will also increase its volume and weight as well as the line loss on the inductor. The larger the inductance value, the longer the dynamic response time and the more serious the waveform distortion. Reducing the inductance can improve the dynamic characteristics, but the current ripple increases, so the value of the inductor must be considered comprehensively. This solution selects the ripple of the inductor current as 30% of the output current Iac

[0057]

[0058] The actual Lf is 5.5mH.

[0059] Output filter capacitor selection

[0060] The function of the filter capacitor is to filter out the high-order harmonics in the voltage together with the filter inductor to ensure the output voltage THD requirements. The larger the Cf, the smaller the THD, the reactive current flowing through the inverter increases, the current flow of the inverter increases, and at the same time, the volume of the system increases and the efficiency decreases. If the filter capacitor is too small, the distortion of the output voltage will increase. The principle of selecting the filter capacitor is to take the value as small as possible while meeting the THD requirement. When selecting the filter capacitor, the reactive current I cf ≤0.5I ac . Iomix is ​​the maximum effective value of the output current.

[0061]

[0062] I cf ≤0.45A because I cf =V sin 2πfC f

[0063]

[0064] At the same time, the cut-off frequency of the filter is not higher than 1KHz.

[0065]

[0066] Get C f ≥4.6u f , the actual Cf is 5uf / 250VAC.

[0067] In order to avoid over-charging of the capacitor when no-load, a resistor RL=100K is connected in parallel at its output end, and finally the power is modulated by the inverter to form an AC voltage signal that meets the requirements at the output end. Inverter rectification technology can achieve high-efficiency power conversion, and provide passive power supply to the switch terminal on the distribution column through inverter rectification. At the same time, a photovoltaic charging module is added to balance the charging and discharging of the lithium battery in real time in the photovoltaic floating charging mode, thereby improving the battery life of the lithium battery.

[0068] The operating frequency of the peripheral circuit parameter design is set at 60kHz, which is achieved by setting the parameters of CT=0.001μF, RT=22kΩ, and RD=470Ω.

[0069] The peripheral circuit parameters are designed to provide 12V to the SG3525A pulse control circuit as its working voltage (its maximum working voltage is 40V) after simple voltage stabilization and filtering of the external input DC power supply. SG3525A can work in a fairly wide frequency range of 60Hz-400KHz. After comprehensive consideration of various factors, we set the working frequency to about 60KHz. That is: CT = 0.001uF, RT = 22KΩ, RD = 470Ω. The formula f = 1 / C T (0.7R T +3R D ) calculation can get the working frequency of the SG3525A pulse control circuit. The positive input pin 2 of the error comparator uses the 5.1V reference voltage (pin 16) generated by the circuit to generate a reference voltage, which is compared with the signal fed back from the DC300V voltage divider after the inverter at pin 1 to adjust the duty cycle of the output pulse, so as to stabilize the 300V output. The pulse output duty of the pulse control circuit SG3525A is adjustable from 0 to 50%. For the shutdown control pin (pin 10), it receives high-level signals from external input, such as overvoltage signals, feedback signals from overcurrent protection circuits, no 300V voltage output signals, deep undervoltage protection signals, etc. Once the above abnormal working phenomena occur, the received high level will stop the SG3525A from working in time, so as not to damage the subsequent output circuits and key components such as the switching power MOS tube, and at the same time reduce the damage to the electrical appliances in use.

[0070] As shown in the figure, CT, RT, and RD determine the circuit's operating frequency of 60KHz. CSS determines the circuit's soft start delay time of about 1.1S. The output feedback from 300V is divided by a resistor and then compared with the reference voltage of pin 2 through the inverting input pin 1 of the error comparator to adjust the width of the output pulse, thereby changing the output voltage. When the voltage at pin 10 is greater than 2.2V, the SG3525A circuit stops working and stops outputting pulses. There are two ways to make pin 10 reach the shutdown voltage. One is that when the input voltage exceeds the preset safety voltage, the internal protection of the circuit is activated, and the setting of the safety voltage can be changed by adjusting the resistor. The other way is from the output of the protection circuit. After the protection circuit is activated, one output is sent to the alarm circuit, and at the same time, one output high level is sent to pin 10 after the resistor voltage is divided, cutting off the operation of the entire main circuit.

[0071] The SG3525A output pulse controls the power MOS tube, uses a push-pull inverter circuit to convert it into high-voltage AC through a high-frequency transformer, and then rectifies it with a bridge rectifier current to output a DC of about 380V.

[0072] The present invention and its implementation methods are described above, and such description is not restrictive. In short, if a person skilled in the art is inspired by it and, without departing from the purpose of the invention, designs structures and embodiments similar to the technical solution without creativity, they should all fall within the protection scope of the present invention.

Claims

1. A passive dedicated device for switch terminals on distribution poles, including a DC / AC inverter circuit, a photovoltaic charging module, a dual power supply switching control circuit, a PWM switch power supply control circuit, and peripheral circuit parameter design. The DC / AC inverter circuit adopts PWM modulation to convert direct current into alternating current through a full-bridge inverter circuit. The photovoltaic charging module adopts a photovoltaic floating charge mode to balance the charging and discharging of lithium batteries in real time to improve the endurance of lithium batteries. The PWM switch power supply control circuit adopts an SG3525A pulse control circuit with an internal reference voltage source, an operational amplifier, and undervoltage protection functions.

2. A dedicated passive device for switch terminals on distribution poles according to claim 1, characterized in that: The DC / AC inverter circuit switch tube is selected as MUR460, and the operating frequency is 20kHz to ensure that the harmonic content of the output voltage is low. The output filter inductor and capacitor are selected as 5.5mH and 5μF / 250VAC respectively to filter out high-order harmonics and ensure the THD requirements of the output voltage.

3. A passive dedicated device for switch terminals on distribution poles according to claim 1, characterized in that: The photovoltaic charging module needs to work in conjunction with the inverter circuit to ensure that the system can still operate stably without an external power supply.

4. A dedicated passive device for switch terminals on distribution poles according to claim 1, characterized in that: The dual power supply switching control circuit is based on the dual power supply backup principle and adopts a passive power supply and a voltage transformer secondary dual power supply backup mode. The main power supply is a passive power supply and the backup power supply is a voltage transformer secondary power supply. When the main power supply fails or fails, the backup power supply automatically takes over the power supply to achieve continuous and stable operation of the system.

5. A dedicated passive device for switch terminals on distribution poles according to claim 1, characterized in that: The PWM switch power supply control circuit adopts the SG3525A pulse control circuit, which has an internal reference voltage source, an operational amplifier and an undervoltage protection function. By adjusting the duty cycle of the output pulse, the output voltage is stabilized at around 300V. When the circuit is abnormal, the control pin is turned off to stop working in time to protect the subsequent output circuit and the switching power MOS tube.

6. A passive dedicated device for switch terminals on distribution poles according to claim 1, characterized in that: The operating frequency of the peripheral circuit parameter design is set at 60kHz, which is achieved by setting the parameters of CT=0.001μF, RT=22kΩ, and RD=470Ω.

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