Medium voltage power transmission system has been in industrial production
has been widely used, such as the petrochemical industry in the pipeline pumps,
the cement industry in the fan and pump stations for water pumps, mechanical
traction transportation industry and metallurgical industry in the mill and so
on. Compared with the low voltage drives, medium voltage drives in many
respects higher technical requirements and challenges. German scholar Holtz in
1977 proposed a three-level inverter circuit topology, where each phase leg
tube with a pair of switches to complement the midpoint box bit. Later, in
1980, the Japanese scholar Nabae continue to develop on this basis, these
auxiliary switch into a pair of diodes, respectively, with upper and lower leg
is connected in series with the midpoint of the head, in order to assist the
midpoint box bit. This circuit is more easily controlled than the former, and
the charge off when subjected to only half the voltage of the DC bus, and
therefore more practical.
Two three-level inverter main circuit design
Three-level inverter main circuit shown in Figure 1. Among them, a phase-shifting transformer △ connection, the secondary side, respectively Y connection and △ connection of two symmetrical windings. Two secondary windings, respectively, after the output of two identical 6-pulse rectifier unit to form 12-pulse rectifier. The 12-pulse rectifiers can produce 6-pulse diode rectifier, low harmonics cancel each other out, thereby reducing the harmonic distortion of grid current, power factor improving network side. In general, the number of pulse wave diode rectifier, the more the output-side current harmonic distortion is smaller. But rarely used in the actual product of more than 30 the number of pulse wave diode rectifier, mainly due to the cost of the transformer will increase a lot, while the performance of the change is not obvious. Therefore, this paper uses 12-pulse diode rectifier.
Diode clamped three-level dc ac inverter main circuit
Seen from Figure 1, each bridge arm of four IGBT, 2 catching diodes and four reverse recovery diode. A phase as an example, when, and or their body diode conduction when the stator voltage of phase A; when and either their body diode conduction, the stator voltage of phase A; when and on-the stator phase A voltage is 0. And can not be simultaneously turned on, a turn-on depending on which phase A load current direction. Thus, for three-level inverter for the AC side voltage, 0, 3 states, three bridge arms are combined, a total of = 27 kinds of switching, ie 27 space voltage vector. The topology of the shortcomings is that: three-level inverter and above the number of devices needed more control and significantly increased the complexity of the neutral point voltage fluctuation.
3 three-level inverter control circuit design
Three-level inverter control system block diagram shown in Figure 2. Including 12 channel IGBT driver circuit, a voltage, a current detecting circuit, the interface processing circuit, DSP control circuit and a human-computer interaction interface.
Three-level inverter control Power energy system block diagram
Wherein, DSP control circuit in accordance with the man-machine interface input parameters and operational mode of the motor command output corresponding PWM drive signals, the drive signal via the interface circuit is processed by the optical fiber transmission to the drive circuit. The drive circuit receives a signal by a dedicated optical fiber of the driver IC 2SD315AI drive IGBT. Voltage and current detection were used LEM produced precision voltage and current Hall Hall. Including the positive and negative bus voltage detection voltage detection and the midpoint voltage detection. Voltage detection circuitry returns the current value via the interface processing circuit DSP given after tuning operation control circuit. When the bus voltage or the midpoint voltage fluctuations outside the allowable range, the protection circuit is activated, the signal blocking IGBT, and through man-machine interface displays the current alarm.
Two three-level inverter main circuit design
Three-level inverter main circuit shown in Figure 1. Among them, a phase-shifting transformer △ connection, the secondary side, respectively Y connection and △ connection of two symmetrical windings. Two secondary windings, respectively, after the output of two identical 6-pulse rectifier unit to form 12-pulse rectifier. The 12-pulse rectifiers can produce 6-pulse diode rectifier, low harmonics cancel each other out, thereby reducing the harmonic distortion of grid current, power factor improving network side. In general, the number of pulse wave diode rectifier, the more the output-side current harmonic distortion is smaller. But rarely used in the actual product of more than 30 the number of pulse wave diode rectifier, mainly due to the cost of the transformer will increase a lot, while the performance of the change is not obvious. Therefore, this paper uses 12-pulse diode rectifier.
Diode clamped three-level dc ac inverter main circuit
Seen from Figure 1, each bridge arm of four IGBT, 2 catching diodes and four reverse recovery diode. A phase as an example, when, and or their body diode conduction when the stator voltage of phase A; when and either their body diode conduction, the stator voltage of phase A; when and on-the stator phase A voltage is 0. And can not be simultaneously turned on, a turn-on depending on which phase A load current direction. Thus, for three-level inverter for the AC side voltage, 0, 3 states, three bridge arms are combined, a total of = 27 kinds of switching, ie 27 space voltage vector. The topology of the shortcomings is that: three-level inverter and above the number of devices needed more control and significantly increased the complexity of the neutral point voltage fluctuation.
3 three-level inverter control circuit design
Three-level inverter control system block diagram shown in Figure 2. Including 12 channel IGBT driver circuit, a voltage, a current detecting circuit, the interface processing circuit, DSP control circuit and a human-computer interaction interface.
Three-level inverter control Power energy system block diagram
Wherein, DSP control circuit in accordance with the man-machine interface input parameters and operational mode of the motor command output corresponding PWM drive signals, the drive signal via the interface circuit is processed by the optical fiber transmission to the drive circuit. The drive circuit receives a signal by a dedicated optical fiber of the driver IC 2SD315AI drive IGBT. Voltage and current detection were used LEM produced precision voltage and current Hall Hall. Including the positive and negative bus voltage detection voltage detection and the midpoint voltage detection. Voltage detection circuitry returns the current value via the interface processing circuit DSP given after tuning operation control circuit. When the bus voltage or the midpoint voltage fluctuations outside the allowable range, the protection circuit is activated, the signal blocking IGBT, and through man-machine interface displays the current alarm.
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