generally use the AC - DC - AC inverter power supply, grid AC into DC rectifier, filter,power inverter, then through the inverter DC into AC power, to Motor power supply. Therefore, the inverter is one of the key technical device. With the development of semiconductor devices, IGBT increasingly being applied to the AC drive technology. The AC drive constituted by the paper mainly analyzes IGBT form, including the main circuit structure of a main circuit of the inverter, the realization of the drive circuit and the snubber circuit protection.
main circuit structure schematic
Figure 1 is a structure schematic diagram of a typical inverter. It consists of three parts: the inverter circuit, driver protection circuit, control and signal acquisition circuit.
inverter circuit is mainly responsible for the electrical energy into the upcoming DC input available for the motor load can be transformed into three-phase alternating current electrical energy to provide energy to the motor. Figure 2 shows the schematic diagram for the inverter circuit, the inverter circuit comprises six insulated-gate bipolar transistor T1 ~ T6 and freewheeling diode D1 ~ D6. T1 ~ T6 through shutdown input DC power by controlling the IGBT tube reverse into a rectangular wave of adjustable frequency AC output to a three-phase motor. Freewheeling diode D1 ~ D6 when T1 ~ T6 is turned off by the conduction reflux to the DC power supply is provided for the regenerative current when the motor braking channel release passage is provided for the electrical energy stored in the motor coil; ,Grid tie inverter.
2 protection the absorption circuit structure
due to the presence of distributed inductance circuit, combined with IGBT switching speed, and contrast when the IGBT is turned off and then the reverse recovery diode reverse-phase recovery, will generate a great surge voltage Ldi / dt thereby threaten IGBT security. Therefore, measures must be taken to suppress the surge voltage to protect the IGBT is not damaged. Retrofitting way to protect absorption circuit can be used to suppress the surge voltage. The schematic in Figure 3, the protection absorption circuit has a good effect of suppressing, having the advantages of a small loss occurred protection absorbent,http://www.gridtieinverter.de/products_show.asp?id=183
2.1 protection circuit schematic analysis
to switch T1 off moment as a starting point for analysis of the absorption circuit works, the course of their work can be divided into: linearization commutation, busbar parasitic the inductance Lp resonance energy absorption capacitance Cs release point of three stages.
linearization commutation stage shutdown signal is received from the switch tube T1 start to the end of full-cutoff switch T1. Flow through the shunt the bus parasitic inductance Lp busbar current through T1 and snubber circuit branch.
switch T1 completely the commutation phase
online after deadline. At this time, the main circuit parasitic inductance Lp and absorption resonant capacitance Cs, Lp the stored energy is transferred to the Cs. When the voltage on the snubber capacitor reaches the maximum value, i.e. the resonance peak, the resonant current i is zero, absorption circuit diode D2 is turned off, the clamping voltage to prevent oscillation.
after the end of the second stage, the absorption overshoot energy discharge through the the absorption resistance R, the power supply and the load capacitance Cs. Approximate that during the discharge process, the load is a constant current source.
2.2 component parameters selected
a. snubber capacitor Cs select
the buffer capacitor Cs
buffer circuit capacitance value:
the
wherein L is the parasitic inductance of the main circuit, the collector current Io for the IGBT is turned off, VCEP eventually reaches a value in the voltage of the buffer capacitor, Ed is the DC supply voltage.
b. the value of the snubber resistor Rs
buffer resistor role in IGBI next before shutdown the buffer capacitor charge to release. IGBT next action before, in 90% of the storage charge discharge conditions, the snubber resistor value formula should satisfy the following formula:
where f is the switching frequency.
3 driver circuit structure
to ensure reliable IGBT operation, the drive circuit plays a vital role.
3.1 IGBT drive circuit requirements
basic requirements
IGBT drive circuit are mainly the following:
(1) the driver circuit must be extremely reliable, to ensure that the charge-discharge circuit to provide a low impedance for the IGBT gate capacitance;
(2) meet the switching characteristics and reactive the consumption allowed case, the gate resistance can be suitably increased, for limiting transient voltage drop spikes;
(3) driving circuit kHz level able to pass a high-frequency pulse signal; < br /> (4) IGBT Gate pole emitter voltage limit voltage drop is ± 20V. Usually selected forward drive voltage is +15 V, and the reverse drive voltage is-8V.
a drive circuit
3.2 M57959L
According to the design principle of the driving circuit, according to different requirements can be designed to various forms of driving circuit. The common driver circuit has a driving circuit of discrete components, and application specific integrated drive circuit. Relative to the drive circuit with discrete components, application specific integrated drive circuit anti-jamming capability, high degree of integration, speed, perfect protection function drive IGBT best.
M57959L hybrid integrated IGBT driver for Japan's Mitsubishi, the internal principle structure shown in Figure 4. It consists of a high-speed optical isolation input, high dielectric strength, compatible with TTL level. Short-circuit protection circuit built-in timing logic and the protection delay characteristics. Negative when the chip is powered by the positive and negative power to overcome the single power supply voltage instability shortcomings, drive power can to drive 200A/600V or 100A/1200V IGBT module. By M57959L a drive circuit shown in Figure 5.
Note gate resistor value should be used. The value of the gate resistor Rext can affect the oscillation suppressing effect, slowing the switch opening when the di / dt, and improve current undershoot waveform to reduce the surge voltage,power inverter. From the safety point of view, should Rext whichever is greater, but the larger the Rext impact switching speed, increasing the switching losses,Grid tie inverter; increase the operating frequency, should take the smaller value. Meet the switching frequency, whichever is greater Rext.
installation and layout of the main circuit
IGBT switching frequency is very fast while the high power IGBT constitute the other parts of the inverter will generate strong interference. These disturbances not only affect the normal working of the circuit, and even may cause the inverter instantaneous short circuit damage. Therefore, pay enough attention to respond to electromagnetic interference, and reasonable installation and layout to reduce electromagnetic interference.
common interference and corresponding measures are:
isolation powered suppression of
(1) IGBT switches interference due to the impact of distributed capacitance and coupling inductance of the power supply transformer, a strong spikes generated when one of the IGBT is turned on or off by the distributed capacitance (inductance) interfere with other the normal work of the IGBT. Accordingly, each of a trigger circuit of the full-bridge inverter must be isolated from the power supply to suppress such interference.
(2) due to the leakage inductance of the average operating current and instantaneous peak current of the inverter, inverter circuit, even a small lead inductance can not be ignored. If not carefully designed PCB layout flux PCB wires through the closed form current. To this end, the following measures can be taken to suppress interference:
a, an IGBT trigger circuit element should be concentrated in a narrow area, avoiding to cross each other;
b, the same phase of the trigger circuit should be adjacent, while the distance between the two groups should be relatively distant;
c, between the PCB and IGBT leads should be as short as possible and mutual stranded.
5 IGBT voltage and current parameters selected
the absorption circuit
in protection, When the the T1 turns, T2 deadline, T2 withstand voltage Uce2 is:
consider grid fluctuations of + / -10%, the T2 ripe voltage Uce2:
take into account the open circuit off instantaneous voltage and IGBT module withstand voltage of 50% to 80% margin should be left in their chosen the module voltage BVce should to:
consider the fluctuations in the grid, the startup current spikes the selected IGBT module Icm for:
wherein, Pn is the inverter output power. δ is the pulse duty ratio, η is the efficiency of the inverter.
6 Conclusion
the
This paper describes the IGBT drive a motor drive circuit, the buffer should pay attention to the problem of absorption composition and parameter selection as well as the main circuit installation and layout of the circuit with the main circuit of the inverter and IGBT parameter selection, the actual application in inverter design value.
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