1 Introduction
The combination of power electronics technology, microelectronic technology and control theory has effectively promoted the development of AC variable frequency speed control technology. In recent years, the application of intelligent IGBTs with drive circuits and protection functions has made the inverter structure more compact and reliable. Compared with other power electronic devices, IGBT has high reliability, easy driving, easy protection, no snubber circuit and high switching frequency. In view of this, develop high voltage IGBT with high voltage, high current and high frequency and apply it to frequency conversion. Devices with higher output voltage levels in the governor have become the focus of attention. The research and development of medium voltage frequency converters is closely related to the development level and application level of power electronic devices such as high voltage IGBT, GTO, IGCT, etc. With the advent of high voltage and high current IGBTs, the medium voltage inverter has been injected with new vitality, Germany. SIMOVERTMV series medium voltage inverter developed by Siemens using high voltage IGBT (600A～1200A/3300V～6500V) and three-level technology has been widely used in the industries of nonferrous metals, metallurgy, electric power, building materials, tap water, petrochemical industry and other users. The recognition of this article on the excellent performance of the fourth generation IGBT, compared with GTO, IGCT and other power electronic devices, combined with the characteristics of MV series medium voltage inverter to discuss the use of three-level technology to obtain excellent output voltage characteristics, using modules In order to meet the needs of various loads, the technology introduces the four-quadrant transmission scheme provided by the three-level active front-end (AFE) technology, and provides a number of application selection examples to illustrate the scheme selection and application effects of the medium-voltage inverter.
2 Comparison of power electronic devices for medium voltage inverters
The development of power electronic devices has experienced thyristor (SCR), turn-off thyristor (GTO), high power transistor (GTR), insulated gate transistor (IGBT) and other stages. At present, atmospheric voltage inverters basically use IGBT to form inverter circuits. In the medium voltage inverter, due to the different circuit structure, the inverter circuit in the AC-DC-AC inverter is basically composed of high voltage IGBT, GTO, IGCT, etc. The unit series multi-level inverter and medium-low-medium inverter The type is mostly composed of low voltage IGBT. The commercialization of the turn-off thyristor GTO in the 1980s promoted the development of AC speed regulation technology. Compared with SCR, it is a self-shutdown device. Due to the elimination of the forced commutation circuit, it is simplified in the AC electric locomotive. Inverter circuit, the current GTO capacity is 6000A/6000V, most of which are used in the speed regulation of electric locomotives (3000~4000) A/4500V, the power range of medium voltage inverter is more than (300~3500) kW, which is relatively small. Power range. The GTO switching frequency is low, which requires a complicated buffer circuit and a gate trigger circuit. The GTO is turned off with a gate negative current pulse, and its value is close to 1/3 of its anode current. For example, if the GTO of 3000A/4000V is turned off, 750A is required. The gate has a negative pulse current, and its gate trigger circuit requires a low inductance circuit in which multiple MOSFETs are connected in parallel, while the same high voltage IGBT requires only 5A of on and off current. The operating frequency of the GTO is lower than 500 Hz. Taking the GTO of 1500 A/4500 V as an example, the turn-on time is 10 μs, and the turn-off time is about 20 μs. The hard-drive GTO (IGCT) is a GTO with a turn-off gain of 1. The GTO manufacturing process is made up of a plurality of small GTO cells connected in parallel. To solve the non-uniform turn-off and cathode current shrinkage effects when turning off GTO, shorten the off The off-time, by increasing the negative gate current rise rate, causes the negative gate current to rise to the magnitude of the anode current within 1 μs, causing the gate-cathode of the GTO to quickly resume blocking. The gate driver composed of GTO external MOSFET is combined into IGCT to realize the function of the field-controlled thyristor. The IGCT process requires the opening and closing process to be as short as possible. The current IGCT maximum level is 4000A/6000V, and the IGCT shutdown process The di/dt buffer is still needed to prevent overvoltage. The IGCT is based on GTO and its operating frequency should be below 1 kHz. With the improvement of shutdown capability and current-carrying capacity, high-voltage IGBTs have a wide application prospect because they have strong self-protection function and do not need to absorb circuits. Since 1988, Siemens has been developing and applying low-voltage IGBTs. It is also a leader in the development of high-voltage IGBTs. For example, the 1200A/3300V IGBTs currently used in the MV series have a gate emitter voltage of only 15V and low trigger power. The turn-off loss is small, and di/dt and dv/dt are effectively controlled. At present, the development level of high-voltage IGBT is (600-1200) A/6500V, and its working frequency is (18-20) kHz.
　 3 characteristics of high voltage IGBT medium voltage inverter
SIMOVERTMV series medium voltage frequency converter adopts the principle of vector conversion field oriented control which has proved excellent performance, namely optimized space vector and pulse width modulation mode, and excellent output voltage characteristics are obtained by applying high voltage IGBT and three level technology. The design has fully considered various load conditions and can be adapted to various applications such as fans, pumps, extruders, hoists, belt conveyors, piston compressors, coilers, and unwinders. Using modular technology to optimize the transmission, 12 or 24 pulse diode rectifiers can be used, or the active end can be used at the input to achieve high dynamic performance, high reliability and optimum price/performance ratio. At present, the voltage source type inverter below 1500kVA basically adopts a two-level circuit structure, and connects the positive pole potential or the negative pole potential of the intermediate DC circuit to the motor. In order to meet the requirements of inverter capacity and output voltage level, and reduce harmonics and dv/dt, a three-level inverter using GTO or high-voltage IGBT appears, and the positive, potential and midpoint potentials of the intermediate DC circuit are sent. The motor goes up. Compared with the two-level inverter, the output waveform has less harmonics, which reduces the loss and reduces the withstand voltage of the power device by half. Siemens uses high-voltage IGBT and three-level technology to develop successful MV series medium voltage inverters. Its inverter circuit requires only 12 or 24 devices at 3300V and 4160V levels. It does not require a buffer circuit and has a compact structure, which improves reliability and overall. effectiveness. The MV series inverters use modular technology to provide a comprehensive solution for various transmission applications. To meet the regenerative braking, the MV series inverters provide active front-end technology, that is, input sinusoidal AC power from the grid to the AFE, and rectify and output DC voltage. And maintaining the required voltage value, the filter circuit ensures that only sinusoidal voltage or current is drawn from the grid and fed back to the grid.
4 MV series medium voltage frequency converter application examples
The evaluation indicators of medium voltage frequency converter include scope of application, design ideas, such as voltage source or current source type, torque ripple, speed control, harmonics and noise, efficiency, power factor and electromagnetic compatibility. MV series inverters achieve extremely high dynamic performance by using optimized space vector and pulse width modulation mode, torque ripple <2%, and perfect control characteristics; fast fuss by harmonic current in various situations Liye analysis can provide typical harmonic current spectrum; MV uses high voltage IGBT without buffer circuit, power factor is greater than 0.96, due to the use of active front-end technology, power factor can be adjusted according to needs (hysteresis or advance), while improving electromagnetic Compatibility meets the requirements for anti-interference. Some application examples are provided below for reference:
(1) In the building materials cement industry, Guangzhou Zhujiang Cement Factory decided to use Siemens MV series products on electric dust collectors, furnace fans and kiln fans after comparing the pressure medium products of several companies. The dust blower motor is Siemens squirrel cage motor 1RQ4506-8, 1300kW/3300V, medium voltage inverter is 6SE8018-1BA00, the input end adopts 12 pulse wave rectification, the total power factor of the inverter is greater than 0î€96; the furnace fan motor is Siemens Squirrel cage motor IRQ4564-6, 2500kW/3300V, inverter is 6SE8031-1BA00; kiln train fan motor is Siemens squirrel cage motor 1RQ4502-6, 1400kW/3300V, inverter is 6SE8018-1BA00, users fully consider the selection The requirements of the high-voltage IGBT inverter on the insulation level of the motor, as well as the system supporting ability of the supplier's motor and inverter, to select the most economical and reasonable solution, the equipment has been put into operation and achieved remarkable energy-saving effects.
(2) In the power industry, SIMOVERTMV has broad application prospects, especially for peaking power plants, the main applications include feed pumps, sending (pushing) fans, mortar pumps, heating pumps and so on. In addition to energy saving, increasing mechanical life and reducing the impact on the power grid, the combustion process of power plant boilers can be greatly optimized, and the power consumption rate of the whole plant is reduced. This is certified in Shandong Longkou Power Plant. The plant has adopted several sets of Siemens inverters for technical transformation, and its SIMOVERTM V1250kW/6kV will also be put into operation very quickly.
(3) In the petrochemical industry, the technical requirements of the extruder in the production of 660,000 tons of high-pressure polyethylene in Beijing Yanshan Petrochemical are as follows: power 3000kW, 1.2 times overload, speed ratio of 1:10 or above (95~950~1150)r /min. It is a typical constant torque load. It is usually driven by a constant speed AC motor or a variable speed DC motor. Considering the long-term operation of the chemical plant, the maintenance workload should be small, and energy saving and other considerations require energy saving and high reliability. Sexual and excellent dynamic performance. After comparison, SIMOVERTMV of Siemens high voltage IGBT and three-level technology is used to meet all requirements, and considering the reduction of harmonic interference to the power grid, the final 4.16kV, 24 pulse wave structure, 3000kW band 6 Complete set of Siemens drive systems for inverter motors (without filters). High-voltage IGBT inverters provide more possibilities for technological transformation and new projects in the petrochemical industry, especially for new projects, where users can choose the best cost-performance ratio.
(4) The application of SIMOVERTMV in the metallurgical industry is increasing, mainly in the following aspects:
1 In the finishing mill, the MV+ squirrel cage machine is used to replace the LCI (load-converting) inverter + synchronous machine scheme, so that the harmonics of the system are smaller and the performance is better. The 5000kWMV finishing mill of Anyang Iron and Steel Co., Ltd. has been commissioned.
2 Replace the DC drive on a cold rolling mill or a crimping machine.
3 In energy-saving applications, it is used in coking fans of steel plants, which usually save more than 30%, such as Maanshan Iron and Steel Company and Handan Iron and Steel Company. In addition, the dust removal fan of the steelmaking plant, because of the shifting condition, can greatly save energy by using the frequency converter, and has been applied in Taiyuan Iron and Steel Company (SIMOVERTMV1250kW).
(5) In the non-ferrous industry, Lingnan Lead and Zinc Group used Siemens MV series products and motors for sulfur dioxide fans and main blowers, taking full account of Siemens' supporting capacity. Among them, sulfur dioxide motor is Siemens squirrel cage motor 1RN4564-4HX60- Z, 2250kW/6000V, the inverter is 12-pulse diode rectification three-level MV6SE8026-1EA00, the main blower motor is 1RN4500-2HV60-Z, 1300kW/6000V, and the inverter is 6SE8018-1EA00.
The combination of power electronics technology, microelectronic technology and control theory has effectively promoted the development of AC variable frequency speed control technology. In recent years, the application of intelligent IGBTs with drive circuits and protection functions has made the inverter structure more compact and reliable. Compared with other power electronic devices, IGBT has high reliability, easy driving, easy protection, no snubber circuit and high switching frequency. In view of this, develop high voltage IGBT with high voltage, high current and high frequency and apply it to frequency conversion. Devices with higher output voltage levels in the governor have become the focus of attention. The research and development of medium voltage frequency converters is closely related to the development level and application level of power electronic devices such as high voltage IGBT, GTO, IGCT, etc. With the advent of high voltage and high current IGBTs, the medium voltage inverter has been injected with new vitality, Germany. SIMOVERTMV series medium voltage inverter developed by Siemens using high voltage IGBT (600A～1200A/3300V～6500V) and three-level technology has been widely used in the industries of nonferrous metals, metallurgy, electric power, building materials, tap water, petrochemical industry and other users. The recognition of this article on the excellent performance of the fourth generation IGBT, compared with GTO, IGCT and other power electronic devices, combined with the characteristics of MV series medium voltage inverter to discuss the use of three-level technology to obtain excellent output voltage characteristics, using modules In order to meet the needs of various loads, the technology introduces the four-quadrant transmission scheme provided by the three-level active front-end (AFE) technology, and provides a number of application selection examples to illustrate the scheme selection and application effects of the medium-voltage inverter.
2 Comparison of power electronic devices for medium voltage inverters
The development of power electronic devices has experienced thyristor (SCR), turn-off thyristor (GTO), high power transistor (GTR), insulated gate transistor (IGBT) and other stages. At present, atmospheric voltage inverters basically use IGBT to form inverter circuits. In the medium voltage inverter, due to the different circuit structure, the inverter circuit in the AC-DC-AC inverter is basically composed of high voltage IGBT, GTO, IGCT, etc. The unit series multi-level inverter and medium-low-medium inverter The type is mostly composed of low voltage IGBT. The commercialization of the turn-off thyristor GTO in the 1980s promoted the development of AC speed regulation technology. Compared with SCR, it is a self-shutdown device. Due to the elimination of the forced commutation circuit, it is simplified in the AC electric locomotive. Inverter circuit, the current GTO capacity is 6000A/6000V, most of which are used in the speed regulation of electric locomotives (3000~4000) A/4500V, the power range of medium voltage inverter is more than (300~3500) kW, which is relatively small. Power range. The GTO switching frequency is low, which requires a complicated buffer circuit and a gate trigger circuit. The GTO is turned off with a gate negative current pulse, and its value is close to 1/3 of its anode current. For example, if the GTO of 3000A/4000V is turned off, 750A is required. The gate has a negative pulse current, and its gate trigger circuit requires a low inductance circuit in which multiple MOSFETs are connected in parallel, while the same high voltage IGBT requires only 5A of on and off current. The operating frequency of the GTO is lower than 500 Hz. Taking the GTO of 1500 A/4500 V as an example, the turn-on time is 10 μs, and the turn-off time is about 20 μs. The hard-drive GTO (IGCT) is a GTO with a turn-off gain of 1. The GTO manufacturing process is made up of a plurality of small GTO cells connected in parallel. To solve the non-uniform turn-off and cathode current shrinkage effects when turning off GTO, shorten the off The off-time, by increasing the negative gate current rise rate, causes the negative gate current to rise to the magnitude of the anode current within 1 μs, causing the gate-cathode of the GTO to quickly resume blocking. The gate driver composed of GTO external MOSFET is combined into IGCT to realize the function of the field-controlled thyristor. The IGCT process requires the opening and closing process to be as short as possible. The current IGCT maximum level is 4000A/6000V, and the IGCT shutdown process The di/dt buffer is still needed to prevent overvoltage. The IGCT is based on GTO and its operating frequency should be below 1 kHz. With the improvement of shutdown capability and current-carrying capacity, high-voltage IGBTs have a wide application prospect because they have strong self-protection function and do not need to absorb circuits. Since 1988, Siemens has been developing and applying low-voltage IGBTs. It is also a leader in the development of high-voltage IGBTs. For example, the 1200A/3300V IGBTs currently used in the MV series have a gate emitter voltage of only 15V and low trigger power. The turn-off loss is small, and di/dt and dv/dt are effectively controlled. At present, the development level of high-voltage IGBT is (600-1200) A/6500V, and its working frequency is (18-20) kHz.
　 3 characteristics of high voltage IGBT medium voltage inverter
SIMOVERTMV series medium voltage frequency converter adopts the principle of vector conversion field oriented control which has proved excellent performance, namely optimized space vector and pulse width modulation mode, and excellent output voltage characteristics are obtained by applying high voltage IGBT and three level technology. The design has fully considered various load conditions and can be adapted to various applications such as fans, pumps, extruders, hoists, belt conveyors, piston compressors, coilers, and unwinders. Using modular technology to optimize the transmission, 12 or 24 pulse diode rectifiers can be used, or the active end can be used at the input to achieve high dynamic performance, high reliability and optimum price/performance ratio. At present, the voltage source type inverter below 1500kVA basically adopts a two-level circuit structure, and connects the positive pole potential or the negative pole potential of the intermediate DC circuit to the motor. In order to meet the requirements of inverter capacity and output voltage level, and reduce harmonics and dv/dt, a three-level inverter using GTO or high-voltage IGBT appears, and the positive, potential and midpoint potentials of the intermediate DC circuit are sent. The motor goes up. Compared with the two-level inverter, the output waveform has less harmonics, which reduces the loss and reduces the withstand voltage of the power device by half. Siemens uses high-voltage IGBT and three-level technology to develop successful MV series medium voltage inverters. Its inverter circuit requires only 12 or 24 devices at 3300V and 4160V levels. It does not require a buffer circuit and has a compact structure, which improves reliability and overall. effectiveness. The MV series inverters use modular technology to provide a comprehensive solution for various transmission applications. To meet the regenerative braking, the MV series inverters provide active front-end technology, that is, input sinusoidal AC power from the grid to the AFE, and rectify and output DC voltage. And maintaining the required voltage value, the filter circuit ensures that only sinusoidal voltage or current is drawn from the grid and fed back to the grid.
4 MV series medium voltage frequency converter application examples
The evaluation indicators of medium voltage frequency converter include scope of application, design ideas, such as voltage source or current source type, torque ripple, speed control, harmonics and noise, efficiency, power factor and electromagnetic compatibility. MV series inverters achieve extremely high dynamic performance by using optimized space vector and pulse width modulation mode, torque ripple <2%, and perfect control characteristics; fast fuss by harmonic current in various situations Liye analysis can provide typical harmonic current spectrum; MV uses high voltage IGBT without buffer circuit, power factor is greater than 0.96, due to the use of active front-end technology, power factor can be adjusted according to needs (hysteresis or advance), while improving electromagnetic Compatibility meets the requirements for anti-interference. Some application examples are provided below for reference:
(1) In the building materials cement industry, Guangzhou Zhujiang Cement Factory decided to use Siemens MV series products on electric dust collectors, furnace fans and kiln fans after comparing the pressure medium products of several companies. The dust blower motor is Siemens squirrel cage motor 1RQ4506-8, 1300kW/3300V, medium voltage inverter is 6SE8018-1BA00, the input end adopts 12 pulse wave rectification, the total power factor of the inverter is greater than 0î€96; the furnace fan motor is Siemens Squirrel cage motor IRQ4564-6, 2500kW/3300V, inverter is 6SE8031-1BA00; kiln train fan motor is Siemens squirrel cage motor 1RQ4502-6, 1400kW/3300V, inverter is 6SE8018-1BA00, users fully consider the selection The requirements of the high-voltage IGBT inverter on the insulation level of the motor, as well as the system supporting ability of the supplier's motor and inverter, to select the most economical and reasonable solution, the equipment has been put into operation and achieved remarkable energy-saving effects.
(2) In the power industry, SIMOVERTMV has broad application prospects, especially for peaking power plants, the main applications include feed pumps, sending (pushing) fans, mortar pumps, heating pumps and so on. In addition to energy saving, increasing mechanical life and reducing the impact on the power grid, the combustion process of power plant boilers can be greatly optimized, and the power consumption rate of the whole plant is reduced. This is certified in Shandong Longkou Power Plant. The plant has adopted several sets of Siemens inverters for technical transformation, and its SIMOVERTM V1250kW/6kV will also be put into operation very quickly.
(3) In the petrochemical industry, the technical requirements of the extruder in the production of 660,000 tons of high-pressure polyethylene in Beijing Yanshan Petrochemical are as follows: power 3000kW, 1.2 times overload, speed ratio of 1:10 or above (95~950~1150)r /min. It is a typical constant torque load. It is usually driven by a constant speed AC motor or a variable speed DC motor. Considering the long-term operation of the chemical plant, the maintenance workload should be small, and energy saving and other considerations require energy saving and high reliability. Sexual and excellent dynamic performance. After comparison, SIMOVERTMV of Siemens high voltage IGBT and three-level technology is used to meet all requirements, and considering the reduction of harmonic interference to the power grid, the final 4.16kV, 24 pulse wave structure, 3000kW band 6 Complete set of Siemens drive systems for inverter motors (without filters). High-voltage IGBT inverters provide more possibilities for technological transformation and new projects in the petrochemical industry, especially for new projects, where users can choose the best cost-performance ratio.
(4) The application of SIMOVERTMV in the metallurgical industry is increasing, mainly in the following aspects:
1 In the finishing mill, the MV+ squirrel cage machine is used to replace the LCI (load-converting) inverter + synchronous machine scheme, so that the harmonics of the system are smaller and the performance is better. The 5000kWMV finishing mill of Anyang Iron and Steel Co., Ltd. has been commissioned.
2 Replace the DC drive on a cold rolling mill or a crimping machine.
3 In energy-saving applications, it is used in coking fans of steel plants, which usually save more than 30%, such as Maanshan Iron and Steel Company and Handan Iron and Steel Company. In addition, the dust removal fan of the steelmaking plant, because of the shifting condition, can greatly save energy by using the frequency converter, and has been applied in Taiyuan Iron and Steel Company (SIMOVERTMV1250kW).
(5) In the non-ferrous industry, Lingnan Lead and Zinc Group used Siemens MV series products and motors for sulfur dioxide fans and main blowers, taking full account of Siemens' supporting capacity. Among them, sulfur dioxide motor is Siemens squirrel cage motor 1RN4564-4HX60- Z, 2250kW/6000V, the inverter is 12-pulse diode rectification three-level MV6SE8026-1EA00, the main blower motor is 1RN4500-2HV60-Z, 1300kW/6000V, and the inverter is 6SE8018-1EA00.
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