Latest Advancements In Power Electronics.

An overview of recent developments in the field of technology for power devices.

Power electronics is a multidisciplinary technology that includes power semiconductor devices, converter circuits, electrical machines, signal electronics, control theory, microcomputers, VLSI circuits, and computer-aided design approaches. Although power electronics experts who are specialized in a specific portion of the spectrum claim to be professionals in this field, a real expert in this field should have some knowledge in all of the aforementioned component fields. This is a difficult task because most of these areas are undergoing rapid technological change. This blog examines progress in several of these major areas, including power semiconductor devices, converter circuits, and power electronics management. These regions’ technological advances have also been emphasized.

Electrical power is processed by power electronics to make it suitable for a wide range of applications, including dc and ac regulated power supplies, electrochemical processes, heating and lighting control, electrical machine drives, induction heating, electronic welding, active power line filtering, static var compensation, and so on. Conversion (dc-ac, ac-dc, dc-dc, and ac-ac) and control employing power semiconductor switches are involved in the procedure. When compared to linear mode power amplification employing power semiconductor devices, switching mode power processing provides improved efficiency at the cost of harmonic ripples on both the load and source sides.

There are essentially two sorts of semiconductor elements in current power electronic equipment: power semiconductors, which may be thought of as the equipment’s muscle, and microelectronic control chips, which give the brain’s power. Both parts are digital, with the exception that one can manage gigawatts of power while the other can only manage milliwatts. In today’s power electronic equipment, the tight coordination of these end-of-the-spectrum electronics provides considerable size and cost benefits as well as a high degree of performance.

Power electronics is now a critical component of every modern country’s industrial sector. Energy conservation, or more efficient use of electricity, is a key part of power electronics applications. In a variable speed heat pump, for example, load-proportional speed modulation of the compressor drive can save up to 30% of energy. The increased cost of power electronics can be recouped in a reasonable amount of time by energy savings, especially in areas where electricity is expensive.

With the introduction of power semiconductor devices, the modem age of power electronics began. Bell Telephone Laboratory created the pnpn triggering transistor in 1956, which was later characterised as a thyristor or silicon-controlled rectifier (SCR) and later commercialised by General Electric Co. Prior to that time, power diodes made of silicon or germanium were accessible. In the three decades since then, power electronics has seen rapid development.

In recent years, power semiconductor devices have seen rapid development. We have never witnessed the birth of so many unusual power semiconductor devices in such a short period of time in the history of PEAD. The core of contemporary power electronics is made up of these components. It is, without a doubt, the most complicated, sensitive, and “fragile” component of a converter. A power electronics engineer must have a complete understanding of the device in order to build a converter that is efficient, dependable, and cost-effective. One noteworthy trend in power electronics is that the cost of silicon-based power and control devices continues to reduce as performance improves, but the cost of passive bulky power elements remains virtually constant. As a result, power electronics experts are seeking a “silicon solution” for passive power circuit components. The employment of resonant and quasi-resonant connection concepts in current switching mode power supply is one example.

An IGBT is a hybrid MOS-gated turn on/off bipolar transistor that combines MOSFET, BJT, and thyristor characteristics. Figure 1 depicts the fundamentals, IGBT construction, as well as its corresponding circuit. The device was commercially introduced in 1983.

Its architecture is similar to that of MOSFET except the n+ layer at the drain has been substituted by a p + layer at the collector. The device has the high input impedance of a MOSFET yet conduction properties similar to a BJT. If the gate is positive with respect to the emitter, an n-channel is induced in the p region. This forward biases the pnp transistor’s base emitter junction, turning it on and producing conductivity modulation in the n-region, resulting in a considerable reduction in conduction drop over a MOSFET.

The “tail current” in a modern IGBT has been significantly reduced by a neutron-irradiated minority carrier lifetime control and by adding the extra n+ buffer layer at the emitter. The device has a higher current density compared to BJT and MOSFET and needs 30 % die size of a MOSFET. Its input capacitance (Ciss) is significantly less than that of a MOSFET. The modem IGBT is available with a 1200-V 400-A power rating. The device is finding popularity and is expected to replace BJT’s in the majority of applications in near future.

An SIT is a high-power, high-frequency device that functions similarly to a triode vacuum tube.

Tokin Corp. was the first company to commercialise SIT in 1987.

The basic construction is shown in Figure 2. It is a short n-channel vertical device where the gate electrodes are buried within the drain and source n-type epi layers. The device is generally on, but if V is negative, the reverse-biased pn junction’s depletion layer will prevent the drain current from flowing.

It is nearly identical to a JFET, with the exception that the vertical and buried-gate structure reduces channel resistance, resulting in a lower drop. Furthermore, decreased gate-source channel resistance reduces gate-to-source negative feedback.

The device has been employed in audio, VHF/UHF, and microwave amplifiers in linear mode. SIT is said to be superior to MOSFET in terms of reliability, noise, and radiation hardness.

Despite the fact that the conduction drop is lower than that of a similar series-parallel MOSFET combination, the extremely large drop makes it unsuitable for ordinary power electronics applications unless a FET-like switching frequency is required.

Japanese universities and industries have used SIT’S in AM/FM transmitters, induction heating, high-voltage low-current power supplies, ultrasonic generators, and linear power amplifiers. Fig.3 shows a 12-kW 100-kHz resonant converter [25] for induction heating and melting

applications.

An SITH, or SI thyristor, is a self-controlling on-off device similar to a GTO. SITH is a device with a minority carrier saturation in the n-region. A depletion layer will stop the anode current flow if the gate is reverse biased with respect to the cathode. Due to the emitter shorting required for high-speed operation, the device does not have reverse blocking capabilities. SITH has a similar turn-off behavior as GTO, in that the negative gate current is substantial and the anode circuit has a tail current.

Ac-dc converter (rectifier), dc-dc converter (chopper), dc-ac converter (inverter), and ac-ac converter at the same (ac controller) . A useful power electronic system will frequently incorporate multiple conversion processes. In terms of size, affordability, reliability, and performance, current advancements in power semiconductor devices and control electronics are having a huge impact on power converter technology.

To convert ac to dc power for applications such as dc drives and electrochemical processes, power electronic converters have traditionally employed thyristors with phase control and ac line commutation. In industrial applications, this type of converter is by far the most common. The majority of today’s converter topologies are remnants of the previous gas-tube era. The phase-control thyristors have symmetric voltage-blocking capabilities and a relatively slow response time. This family of converters, on the other hand, has a very simple control scheme and a high efficiency.

Thyristor or triac-based ac voltage controller (same output frequency) using the phase control principle is popularly used in light-dimming control, heating control, and single-phase appliance-type drives. Phase-controlled cyclo-converters are used in VSCF (variable speed constant frequency) aircraft-generating systems and large-capacity ac drives. The inherent harmonics and lagging var problems due to phase control are also present here. APLC’s, as described before, are active tools to combat these problems. The cycloconverters can be operated in circulating current mode with programmable magnitude of current so that the input-lagging var remains fixed regardless of load variation.

DC-DC converters convert unregulated dc voltage to a regulated or programmable dc voltage at a different level and are commonly used in dc motor drives and switching mode power supplies (SMPS). The conventional PWMtype converter (also known as a chopper) can be classified as buck, boost, or buck-boost type. A single-quadrant drive uses a buck converter, a two-quadrant drive uses buck and boost types in combination, and a four-quadrant drive uses an H bridge that provides buck and boost functions for either direction of rotation. High-power converters normally use BJT, IGBT, or GTO switches with switching frequencies up to several kilohertz, whereas low-power low-voltage converters use power MOSFETs at much higher frequencies

Inverters can be generally classified as voltage-fed and current-fed types and are mainly used in ac motor drives, UPS systems, APLC systems, and induction heating. The voltage-fed type is by far the most popular for industrial applications. A PWM voltage-fed inverter system for a drive generally uses a diode rectifier in the front end and therefore this system does not have regenerative feedback capability. The PWM control of the inverter regulates the voltage magnitude and harmonic ripple at the output. Both sinusoidal voltage PWM and hysteresis-band current-control PWM methods are widely used.

Microcomputer control is preferred in a sophisticated power electronics system, such as an electrical machine drive, HVDC converter, or UPS system. There are various advantages of using a microcomputer for control. It reduces control hardware costs significantly, enhances system reliability, and eliminates drift and electromagnetic interference (EMI) issues. The hardware can be universally designed, but the software can be flexible, allowing it to be changed or upgraded when the system’s requirements change. Additional advantages of microcomputer control include data storage, monitoring, diagnostics, and hierarchical control capability.

Because the system variables are usually analog in nature, the microcomputer interfaces with the physical system through AD/DA converters in real-time control applications. Thyristor gate firing control, closed loop control, digital filtering, nonlinearity compensation, PWM control, sequencing control, monitoring and warning, data collecting, diagnostics, and so on are all examples of general control tasks in a power electronics system. Performance optimization through on-line search, on-line parameter and state estimates, optimum and adaptive control, fault tolerant control, and other advanced microcomputer capabilities may be included. The software functions are initially recognised and organised into separate jobs based on sample intervals in the design of microcomputer control. The executive software executes the application procedures under different tasks in order based on their priority. The sequencing function is an important task that is controlled by a microcomputer.

Power consumption is a burning issue in high performance systems based on deep submicron (DSM) processors (CPUs and GPUs). Resonant circuit operation for power consumption improvements in high speed clocking applications has been extensively studied. The energy used to charge the clock grid node each period can be recycled within the LC resonant tank network formed by the large global clock capacitance and integrated inductors. Novel integration of resonant circuits that can save several watts of power across the Dynamic Voltage and Frequency range.[3]

A VLSI chip is typically characterised as one that contains more than 100 000 devices. It’s a working chip that can be used alone or in conjunction with other VLSI chips, such as microcomputers. Reduced cost for high-volume applications, increased speed due to parallel signal processing, improved reliability, and low power consumption are all advantages of VLSI control. Application-specific integrated circuits (ASICs) based on semi custom CMOS VLSI are becoming increasingly common. The gate-array IC, which consists of a matrix of many NAND or NOR gates, is the most prominent member of this family. The gates, as well as a few analogue devices, are wired to accomplish a specific task. A programmable gate-array circuit allows for the creation of flexible logic systems that can be erased and reprogrammed in the same way that an EPROM can. On the same chip, a counter, decoder, RAM, ROM, microcontroller, AD/DA converter, op amp, comparator, and other functioning digital and analogue elements are found.

The whole functioning circuit is created by selecting and interconnecting the necessary components from the library. A standard-cell ASIC provides better performance while using less chip “real estate.”[1]

Artificial intelligence (AI) approaches, particularly neural networks, have recently had a big impact on power electronics and motor drives. Neural networks have opened up a new and exciting frontier in the field of power electronics, which is already a complicated and diverse subject that has been evolving rapidly in recent years. Nonlinear function generation, delay less filtering and waveform processing, vector drive feedback signal processing, space vector PWM of two-level and multilevel inverters, adaptive flux vector estimation, and some of their combinations for vector-controlled ac drive are some of the application examples. Based on the present technological trend, neural networks appear to have a wide range of applications in power electronics and motor drives in the future.[2]

We would like to thank our mentor Prof. Bharat Tarlekar for giving us the opportunity to explore the world of recent advancements in power technology, we would also like to thank him for his constant support and insights in the process of compilation of this blog.

[1] Recent Advances in Power Electronics -Bimal K. Bose

[2] Neural Network Applications in Power Electronics and Motor Drives — An Introduction and Perspective Bimal K. Bose

[3]Power Electronics in VLSI : Design Challenges and Solutions- Ignatius Bezzam

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