Voltage sag protection equipment for middle-high voltage direct current load

Abstract

The utility model discloses a voltage sag protection device used for a medium and high voltage DC load, comprising six Boost DC / DC converters which are interleaved and connected in parallel, a driving circuit, a pre-charging circuit, a single-chip microcomputer control circuit and an output diode, and the output end of the single-chip microcomputer control circuit is connected with the input ends of the driving circuit and the pre-charging circuit. The output ends of the driving circuit and the pre-charging circuit are connected with the input end of the six-path interleaved Boost DC / DC converter, and the output end of the six-path interleaved Boost DC / DC converter is connected with the output diode. The converter can be used for a medium-high voltage frequency converter, a six-path interleaved Boost topological structure can reduce current stress of power tubes, facilitates selection of low-current and high-performance power tubes (the type selection of the power tubes is wider) by a circuit, can reduce ripple of total output current, prolongs the service life of an output capacitor, increases the power density of the converter, and improves the conversion efficiency of the converter. Higher switching frequency is allowed, and the overall efficiency is improved.

Description

Technical Field

[0001] This utility model relates to a frequency converter control system for industrial sites, specifically a medium- and high-voltage voltage sag protection device. Background Technology

[0002] Complex and precision equipment widely used in modern industry (such as frequency converters) is highly sensitive to power quality issues. Over 90% of power quality problems stem from voltage dips. Once a voltage dip or fluctuation occurs, it can lead to downtime or even malfunctions, causing severe disruption to production and significant economic losses. Therefore, voltage dips are considered one of the most significant power quality problems affecting the normal and safe operation of electrical equipment. Strengthening the prevention and control of power quality problems is particularly important during the energy structure transition to new energy sources.

[0003] Currently available voltage sag protection devices for DC loads can only protect low-voltage frequency converters. However, an increasing number of medium- and high-voltage frequency converters are operating in industrial settings. Furthermore, existing voltage sag protection devices are bulky, have low power density, narrow temperature range, and short lifespan, thus increasing costs. To address the shortcomings of existing voltage sag protection devices—their inability to protect medium- and high-voltage frequency converters from voltage sags and their large size and short lifespan—this paper proposes a voltage sag protection device specifically for medium- and high-voltage DC loads. Utility Model Content

[0004] Purpose of this utility model: The purpose of this utility model is to provide a voltage sag protection device for medium and high voltage DC loads, solving the problems of poor voltage sag resistance of medium and high voltage frequency converters, and low power density, large size, and narrow temperature range of existing voltage sag protection devices.

[0005] Technical Solution: To achieve the above objectives, the present invention provides a voltage sag protection device for medium- and high-voltage DC loads, comprising six interleaved parallel Boost DC / DC converters, a drive circuit, a microcontroller control circuit, and output diodes. The output terminal of the microcontroller control circuit is connected to the input terminal of the drive circuit, and the output terminal of the drive circuit is connected to the input terminal of the six interleaved parallel Boost DC / DC converters. The output terminals of the six interleaved parallel Boost DC / DC converters are connected to the output diodes. The microcontroller control circuit outputs six PWM signals to control the operating state of the six interleaved parallel Boost DC / DC converters through the drive circuit.

[0006] It also includes a pre-charging circuit. The input of the pre-charging circuit is connected to the output of the microcontroller control circuit, and the output is connected to the output capacitor of the six interleaved parallel Boost DC / DC converter. The microcontroller control circuit pre-charges the output capacitor of the six interleaved parallel Boost DC / DC converter through the pre-charging circuit.

[0007] It also includes an RS-485 communication interface and a human-machine interface; the human-machine interface is connected to the microcontroller control circuit via the RS-485 interface.

[0008] The capacitors used at the output of the six-channel interleaved parallel Boost DC / DC converter are thin-film capacitors.

[0009] The microcontroller control circuit uses the TMS320F28034 microcontroller.

[0010] The power transistors of the six interleaved parallel Boost DC / DC converters are all discrete MOSFET switches.

[0011] Beneficial effects: The present invention has the following advantages: 1. The high voltage sag protection device of the present invention achieves voltage boost through a six-channel interleaved parallel Boost DC / DC converter, which not only reduces the current stress of the power transistors, allowing the circuit to select low current, high performance power transistors (thus broadening the selection range of power transistors), but also supports higher switching frequencies. In addition, this design effectively reduces the ripple of the total output current and the capacitance of the Boost DC / DC converter output capacitor, thereby reducing the size of the device, increasing the power density of the converter, and significantly improving the overall efficiency.

[0012] 2. The output capacitor of the DC / DC converter adopts a film capacitor, which has advantages such as non-polarity, low equivalent series resistance, high temperature stability, long service life, high efficiency and high reliability compared with the electrolytic capacitor used in existing voltage sag protection devices. It can adapt to high frequency circuits and wide temperature environment, effectively enhancing the stability and reliability of the DC / DC converter.

[0013] 3. The high voltage sag protection device adopts digital control technology to realize programmable output, faster and more sensitive human-machine interaction response, and can work in DC power supply mode to output stable medium and high voltage DC power, providing stable working voltage for medium and high voltage frequency converters and ensuring safe and stable system operation.

[0014] 4. The high-voltage voltage sag protection device has a simple structure and is easy to operate. It can effectively ensure the normal and stable operation of the frequency converter and provide users with an efficient and reliable voltage protection solution. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the voltage sag protection device.

[0016] Figure 2 This is a topology diagram of a voltage sag protection device.

[0017] Figure 3 The circuit topology diagram of a six-channel interleaved parallel Boost DC / DC converter;

[0018] Figure 4 This is the main control flowchart of the microcontroller control circuit. Detailed Implementation

[0019] The technical solution of this utility model will be described in detail below with reference to the embodiments and accompanying drawings.

[0020] like Figure 1 As shown, this utility model is a voltage sag protection device for medium- and high-voltage DC loads in medium- and high-voltage frequency converters. It includes six interleaved parallel Boost DC / DC converters, a drive circuit, a pre-charge circuit, a microcontroller control circuit, and output diodes. The output of the microcontroller control circuit is connected to the inputs of the drive circuit and the pre-charge circuit. The output of the drive circuit is connected to the input of the six interleaved parallel Boost DC / DC converters. The output of the pre-charge circuit is connected to the output capacitor of the six interleaved parallel Boost DC / DC converters. The output of the six interleaved parallel Boost DC / DC converters is connected to the output diodes. The output capacitors of the DC / DC converters are film capacitors. This utility model also includes an RS-485 communication interface and a human-machine interface. The human-machine interface is connected to the microcontroller control circuit via the RS-485 interface, and remote intelligent control can also be performed through the human-machine interface and the RS-485 communication interface.

[0021] like Figure 2As shown, the microcontroller control circuit of the high-voltage voltage sag protection device in this utility model uses a 24V power supply and a TMS320F28034 microcontroller chip. Compared with the PIC16F72, it achieves programmable output, more convenient human-machine interaction, and faster response. The microcontroller control circuit integrates an AD sampling circuit, a temperature sampling circuit, an RS-485 communication interface, CAN communication, and a six-channel PWM signal transmission interface. The AD sampling circuit and temperature sampling circuit are used to collect the DC / DC converter output voltage, inductor current, and ambient temperature; the RS-485 communication interface is used for communication with the human-machine interface; the six-channel PWM signal transmission interface is used to send PWM signals to the drive circuit to control the operating state of the DC / DC converter. Simultaneously, the microcontroller control circuit controls the pre-charge circuit to pre-charge the output capacitors in the six interleaved parallel Boost DC / DC converters, preventing inrush current from the output capacitors at power-on, which could damage capacitors, power transistors, and other components. This utility model's high-voltage voltage sag protection device uses a DC power supply (battery pack) for power supply. The battery pack serves as the input energy source for the six interleaved parallel Boost DC / DC converters in the protection device. The magnitude of the converter's input voltage is determined by the number of batteries connected in series. The battery pack voltage is boosted by the six interleaved parallel Boost DC / DC converters and connected to the DC bus of the frequency converter through the output diodes.

[0022] like Figure 3 As shown, the six-channel interleaved parallel Boost DC / DC converter uses a microcontroller control circuit as the controller. Based on the compared and acquired actual output voltage and inductor current with the reference output voltage and inductor current, it generates a PWM duty cycle and transmits the PWM signal to the drive circuit to control the on / off state of each switch in the DC / DC converter. The six power switches Q1, Q2, Q3, Q4, Q5, and Q6 have equal duty cycles, and each switch lags the previous switch by one-sixth of a switching cycle. Compared to a single Boost DC / DC circuit, the interleaved parallel Boost topology reduces the current stress on the power transistors, allowing for the selection of low-current, high-performance power transistors, permitting higher switching frequencies, reducing the ripple of the total output current, decreasing the output capacitor capacity of the Boost DC / DC converter, reducing the device size, increasing the converter's power rating, and effectively improving overall efficiency. The output capacitor uses a thin-film capacitor, which has advantages such as non-polarity, low equivalent series resistance, high temperature stability, high efficiency, and high reliability, making it suitable for high-frequency circuits and wide-temperature environments, effectively enhancing the stability and reliability of the DC / DC converter. Among them, U... in U is the input voltage. oFor the output voltage, the first Boost DC / DC circuit consists of C1, L1, Q1, D1, and C2, where L1 is an inductor, C1 and C2 are film capacitors, power transistor Q1 is a discrete MOSFET switch, and diode D1 is a fast recovery diode. The second Boost DC / DC circuit consists of C1, L2, Q2, D2, and C2, where L2 is an inductor, power transistor Q2 is a discrete MOSFET switch, and diode D2 is a fast recovery diode. The remaining four Boost DC / DC circuits are constructed in the same way as the first two.

[0023] like Figure 4 As shown, in DC power supply mode, the input voltage of the DC power supply is usually required to be lower than the output voltage of the Boost DC / DC converter. The output voltage and inductor current of the DC / DC converter are collected by the microcontroller control circuit. Then, the microcontroller calculates the PWM duty cycle of the interleaved parallel Boost DC / DC converter power transistors through the program and transmits the PWM signal to the drive circuit. The drive circuit controls the interleaved parallel Boost DC / DC converter to start working (where the duty cycles of the six power transistors Q1, Q2, Q3, Q4, Q5, and Q6 are equal, and each switch turns on after the previous switch by one-sixth of a switching cycle), so as to achieve the voltage boosting effect. Its output is a stable medium-high voltage DC power. When the AC input voltage of the frequency converter is normal, the inverter bus voltage is greater than the output voltage of the medium-high voltage sag protection device (HVSP), the output diode is reverse-biased and the HVSP is in standby mode. When a voltage sag occurs in the AC mains, the DC bus voltage of the frequency converter drops. At this time, the output diode is forward-biased, so the medium-high voltage DC power output from the interleaved parallel Boost DC / DC converter is sent to the DC bus of the frequency converter to provide voltage support, ensuring that the frequency converter will not stop due to the drop in AC voltage. The HVSP module plays a role in providing voltage support for the frequency converter. At the same time, a current sensor is used to detect the output inductor current. The current is collected by the microcontroller control circuit and sent to the microcontroller for processing. When the HVSP device detects the output inductor current, the microcontroller starts the support timing. When the AC mains voltage returns to normal, the output diode is reverse-biased and the output inductor current is zero. The microcontroller stops the timing, and the HVSP automatically exits support, preparing for the next voltage sag or power outage.

[0024] This utility model's medium- and high-voltage voltage sag protection device can automatically activate when a voltage sag occurs in the AC power grid, and automatically deactivate after the power grid returns to normal, allowing the AC power grid to power the frequency converter again. Furthermore, when the required load power is small, a single protection device can operate independently; when the required load power is large, multiple protection devices can be connected in parallel. In this case, the output terminals of the multiple protection devices connected in parallel are connected to the DC bus of the frequency converter, and no circulating current will occur.

Claims

1. A voltage sag protection device for medium- and high-voltage DC loads, installed between the DC power supply and the DC bus of the frequency converter, characterized in that: The system includes a six-channel interleaved parallel Boost DC / DC converter, a drive circuit, a microcontroller control circuit, and output diodes. The output of the microcontroller control circuit is connected to the input of the drive circuit, and the output of the drive circuit is connected to the input of the six-channel interleaved parallel Boost DC / DC converter. The output of the six-channel interleaved parallel Boost DC / DC converter is connected to the DC bus of the inverter through the output diodes. The microcontroller control circuit sends six PWM signals to control the operating state of the six-channel interleaved parallel Boost DC / DC converter through the drive circuit. It also includes a pre-charging circuit. The input of the pre-charging circuit is connected to the output of the microcontroller control circuit, and the output is connected to the output capacitor of the six interleaved parallel Boost DC / DC converter. The microcontroller control circuit pre-charges the output capacitor of the six interleaved parallel Boost DC / DC converter through the pre-charging circuit.

2. The voltage sag protection device for medium and high voltage DC loads according to claim 1, characterized in that: It also includes an RS-485 communication interface and a human-machine interface; the human-machine interface is connected to the microcontroller control circuit via the RS-485 interface.

3. The voltage sag protection device for medium and high voltage DC loads according to claim 1, characterized in that: The capacitors used at the output of the six-channel interleaved parallel Boost DC / DC converter are thin-film capacitors.

4. The voltage sag protection device for medium and high voltage DC loads according to claim 1, characterized in that: The microcontroller control circuit uses the TMS320F28034 microcontroller.

5. The voltage sag protection device for medium and high voltage DC loads according to claim 1, characterized in that: The power transistors of the six interleaved parallel Boost DC / DC converters are all discrete MOSFET switches.

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