trends in the global green energy, more and more household appliances, lighting equipment, power tools, uninterruptible power systems (UPS), and other industrial equipment began to use solar power, solar energy conversion is required alternating current (AC) or direct current (DC) voltage.
To produce these devices required voltage and current to the high efficiency, the power inverter needs to be properly combined controller, drive, and the output power devices. This article discusses this DC-to-AC inverter design, optimized specifically for single-phase sine wave output of 500W power, 120V and 60Hz frequency. 200V DC input of this design can be generated by the DC / DC voltage converter connected to the solar array battery panels.
for such applications, there are a variety of advanced power devices can be used,www.12vgridtiepowerinverters.com, such as a MOSFET, a bipolar junction transistor (BJT) and IGBTs. However, in order to obtain the best conversion efficiency and performance, choose the right power for this solar inverter transistor challenging and very time-consuming.
years of studies show that the IGBT can provide more advantages than any other power device, which includes a greater current handling capability, with the voltage (rather than the current) is easily realized gate control, as well as integrated in the package ultra fast recovery diodes to achieve faster turn-off time.
IGBT, is a minority carrier device, it is the off time of the re-combination of speed depends on the minority carrier With the recent improvement of process technology and device structure, its switching characteristics have been significantly enhanced ,Grid tie inverter. In addition, IGBT with ultra-high performance and wide conduction safe operating area (SOA), the work is very stable. Based on these advantages, this article describes the power inverter choose IGBT as a power switch.
power inverters generally use the full-bridge topology, this solar inverter design uses four high-voltage IGBT (Figure 1). The transistors Q1 and Q2 are used as high-pressure side IGBT, Q3 and Q4 are used as a low voltage side power device. In order to maintain a low total power loss low and high power conversion efficiency, the DC / DC inverter solutions take advantage of the low pressure side and high-side IGBT frequency to 60Hz single-phase AC pure sine waveform. Another article written by the author also describes how to correct selection of high-voltage IGBT for such solar inverter applications.
switching IGBT
essence, in order to maintain the harmonic component is low and minimum power loss, the high voltage terminal of the inverter the IGBT using pulse width modulation (PWM), the low voltage side IGBTs are 60Hz frequency converting current direction. IGBT PWM frequency from 20kHz or more than 20kHz, and 50/60Hz modulation scheme by letting the high voltage terminal, the output inductor L1 and L2 in the examples can be made very small, and can still efficient filtering of harmonic components. In addition, the noise could be heard from the inverter is small, because the switching frequency is higher than the frequency of human auditory.
compare various switch technologies, and IGBT found to obtain the best combination of minimum power loss and maximum inverter performance the use of ultra-fast-channel type IGBT transistor of the high-pressure side, the use of the standard speed of the low voltage terminal transistor planar process IGBT ( Figure 2).
with rapid and standard speed planar devices, the switching speed of 20kHz ultra-fast channel the IGBT can provide the lowest total conduction losses and switching power loss. Similarly, for the low-voltage side switching circuit, 60Hz standard speed IGBT can provide the lowest power loss.
ultra-fast channel IGBT switching characteristics of study high-voltage (600V) can be clearly found that these devices work with the best performance in 20kHz. These devices can provide minimal switching losses at these frequencies, including lower collector-to-emitter saturation voltage (VCE (on)) and the total switching energy (ETS), so that the total conduction losses and switching power loss kept to a minimum . Therefore, the high-pressure side power devices usually use ultra-fast channel type IGBT such as IRGB4062DPBF.
fact, power inverter , is to further reduce the switching power loss in the same package, IRGB4062DPBF also integrates an ultra-fast soft recovery diodes. Transistor switching frequency of the high-pressure end of the election in 20kHz Another benefit is the output inductor can be made very small, so that the harmonic components of the filter is very easy. In addition, these IGBT does not require the short-circuit rates, as when the inverter output is shorted, the output inductor L1 and L2 will be limited to the current di / dt, leave a sufficient reaction time and thus to the controller.
In requirements IGBT short circuit rate can be higher than the same size of the short-circuit rate IGBT VCE (on) and higher ETS. Thus, the short-circuit rate requirements IGBT power loss would be bigger, and thus reducing the efficiency of the power inverter.
lower conduction and switching losses in the same package, higher current density, ultra-fast trench IGBT square reverse bias workspace and 175 ° maximum junction temperature, and able to withstand four times the rated current.
with high-end devices, the conduction losses are the main factors of the low voltage side IGBT. Switching losses of these devices is not obvious because the operating frequency of the low-pressure end of the transistors only 60Hz. The standard speed plane IGBT devices specifically optimized for low frequency and low conduction losses. Therefore, when the low-pressure end of the device switching frequency is 60Hz, the low-pressure end devices can use the standard speed of the plane IGBT to achieve the lowest power loss. http://www.gridtieinverter.de/
switching losses of these devices, so it will not affect the the standard speed planar IGBT total power loss. The standard speed IGBT IRG4BC20SD is the correct choice of the low voltage side of the power devices.
package integrated ultra-fast, soft recovery anti-parallel diode fourth-generation IGBT been optimized for minimum saturation voltage and low operating frequencies (<1kHz), typical VCE (on) at a current of 10A. is 1.4V. The same package diode connected across the low voltage terminal IGBT has a particularly low forward voltage drop and reverse leakage current, allows freewheeling (freewheeling) and during the reverse recovery loss minimum.
switching technology This design has the following advantages: high-pressure end, with the package soft recovery diode independently optimized to achieve high efficiency by allowing the high-pressure side and low-side IGBT; freewheeling time, eliminating unnecessary switch loss; IGBT switching frequency of the low voltage terminal of only 60Hz, conduction losses are the main factors for these IGBT; no cross-conduction, because any point in time switches have occurred in the right angle on two devices (Q1 and Q4, or Q2 and Q3); bus straight through the possibility does not exist, because the same edge of the bridge IGBT switch can never be in a complementary manner; jumper low-side IGBT with the package, the ultra-fast, soft recovery diode allows optimized freewheeling and anti- minimum loss to the recovery period.
features and performance
in the system-level power in the inverter circuit, each side of the H-bridge using a high voltage, high-speed gate drive IC for driving, and the IC has a separate channel of the reference output of the low voltage side and high voltage terminal (Fig. 3) . Drive IRS2106SPBF floating channel allows the bootstrap supply operation of the high-pressure end of the power transistor, Grid tie inverter .
Therefore, the high-side driver is no longer need for a separate power supply, which not only improves the efficiency of the inverter, but also reduces the number of devices of the entire system. Obsolete when the the diode flow of current on the low voltage side IGBT same package, drive bootstrap capacitor will be refreshed every switching cycle.
because of the high-pressure end of Q1 and Q2 the same package diode will not freewheeling through, mainly on the low-pressure end of Q3 and Q4 diode conduction losses, switching losses are very small, so the total system losses have been minimized, and the system efficiency maximized. The possibility of cross-conduction is also excluded, because any point in time the switch only occurs on the right angle of the two devices (Q1 and Q4, or Q2 and Q3).
Additionally, each output driver IC has a large pulse current cache level circuit, they are designed for reducing the cross guide of the drive-pass possibilities. System work in a single DC bus power, without negative DC bus. For the system as a whole, all these factors have led to a more efficient and less number of devices.
inverter design, +20 V power supply for the first time be used to supply to the microprocessor and control circuits. PIC18F1320 microcontroller used in the program of this inverter 8 will IGBT driver to achieve the source code, to provide a signal, and then from these IGBT drive ultimately generates a drive signal to drive the IGBTs.
Speaking of the drive, where the need to introduce. Design low end and the high-pressure side IGBT drive and free latch CMOS technology manufactured using patented advanced high-voltage IC process (G5 HVIC), the maximum operating voltage of up to 600V. They also use a high-voltage level conversion and terminating techniques to generate the appropriate gate drive signals from the low voltage input from the microcontroller. Drive logic inputs are compatible with standard CMOS or LSTTL output, the lowest level to 3.3V logic.
ultra fast diodes D1 and D2 provide a charging path to the capacitors C2 and C3, and to get the correct power supply to ensure that the high-pressure side drive. Within a half cycle of positive output, the high-pressure-side IGBT Q1 is sinusoidal PWM modulation, while the low voltage terminal Q4 keep the conduction state (Fig. 4). Similarly, in the half cycle of the negative output, the high voltage terminal Q2 sinusoidal PWM modulation, while the low voltage terminal Q3 remains turned on. This switching technology will be a 60Hz AC sine wave generated behind the output LC filter capacitor C4.
This inverter design output power is 500W, and the AC power output is the actual measured 480.1W, the power loss of 14.4W. 60Hz AC output voltage is 117.8V, and the output current of 4.074A. Figure 5 is the the 500W design output 60Hz waveform.
on the apparatus measured the efficiency is 97.09%. Uses a similar device, the inverter is adjusted to 200W output, and its conversion efficiency was measured again. The load on the AC power is 214W, the power loss of 6.0W. 60Hz output voltage is 124.6V, the output current is 1.721A. The measurement obtained in the rated power conversion efficiency of 97.28%. It has been observed at the lower output power (100W) can also be achieved equally efficient performance.
Figure 6 shows the measured output power level of from about 100W to 500W inverter power loss,power inverter. Show that it can be maintained in a very wide range of output power for the high output efficiency better than 97%, even if the power loss becomes large as the output power, the measurement of the efficiency of the inverter in the same output power range, under the same DC input (Figure 7).
In short, under the correct combination of the drive and the end of the high and low voltage IGBT, this solar inverter design in the output power range close to the range from about 100W to 500W, and can provide the same high power conversion efficiency performance. Due to high efficiency, low power loss will not bring any thermal management challenges, therefore, installed drives and high-voltage IGBT demo board can work to 500W fanless.
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