Three-level active power filter technology details
Diode-clamped three-level topology was proposed by Japanese scholar Nabae.A in 1980, and has been widely used in various fields of power electronics technology after nearly 30 years of development. The advantage of diode-clamped three-level topology is that the reverse voltage of each switching tube is half of the DC bus voltage, and the converter of a higher voltage class can be composed of a switching tube of a lower voltage class. This technology is now widely used in medium voltage high power AC drive systems. Three-level medium-voltage frequency converters with 6500V grade IGBT or IGCT have been widely used in 4.2kV motor drive systems. Generally, the three-level technology is generally used in the system with high voltage and high power, which is determined by the contradictory reality of the limited voltage withstand of the power device and the high demand voltage of the converter system. But we should see some advantages inherent in the diode-clamped three-level topology itself.
(1) With a lower voltage level of the switching tube to form a higher voltage level of the converter, with the continuous development of power device technology, there are 6500V IGBT sold on the market, but the higher the voltage of the IGBT the higher the switching loss, the highest switching frequency has become relatively low. The IGBT switching frequency above 3300V will not exceed 5kHz, and the switching loss of 1200V IGBT is much greater than that of 600V IGBT. The switching loss of the three-level converter using low-voltage IGBT is much lower than that of the two-level converter using high-voltage IGBT with the same voltage level, and the switching frequency can be achieved by the former is also higher than that of the latter.
(2) Can output three levels. Diode-clamped three-level converters can output positive bus voltage, negative bus voltage and zero voltage (referred to as P, N, O), under normal circumstances, the output voltage jumps between P-O and O-N, and in special cases, P-N jumps, while the two-level converters can only jump between P-N. That is to say, the voltage jump amplitude of the three-level is half of the DC bus voltage, and the two-level is the DC bus voltage. High voltage jump amplitude brings higher ripple current to grid-connected inverter or active power filter. In order to suppress ripple current, larger output inductance and filter capacitance are needed, which brings higher ripple current loss. At the same time, the output filter inductance capacitor also reduces the current response speed, or has a certain limit on the output current ability. For the inverter, it is the impact on the motor and the larger shaft current, which seriously affects the life of the motor. In addition, the higher voltage jump amplitude will also produce serious electromagnetic interference, which will also cause serious harm to the surrounding electronic equipment. And the three-level with its inherent advantages, to a large extent to solve the above problems.
With the continuous development of technology, three-level technology has been paid attention to by more and more people, and it has also been introduced into the low-voltage and low-power applications of 400V in the field of medium voltage and high power. Various internationally renowned power device manufacturers have launched a large number of integrated diodel-clamped three-level power modules adapted to the application of 400V systems, and have gradually replaced the traditional two-level converters. Successful three-level products for use in the 400V field are as follows:
(1) In 2008, Yaskawa Electric launched the Varispeed G7 series of universal vector inverters, and its 400V products adopted Mitsubishi’s three-level power module, and achieved great success in application.
(2) In 2009, Dezhou Heleng Industrial Automation Co., Ltd. launched HEINV series three-level photovoltaic grid-connected inverter on the basis of self-developed three-level converter control technology. The front-end adopts symmetric BOOST for maximum power point tracking, and the inverter adopts diode-clamping three-level topology. The three-level power module with Semikron is superior to similar two-level products in every index.
(3) In 2009, Dezhou Heleng Industrial Automation Co., Ltd. launched the industry’s first three-level active power filter HESINE series products, and achieved great success. This article will do a more detailed description of this series of products.