AC waveform, where the output voltage and frequency can be set arbitrarily. Fig 1: Classification of three-phase AC-Ac dc machines pdf converter circuits.
In VSI converters, the rectifier consists of a diode-bridge and the DC link consists of a shunt capacitor. In CSI converters, the rectifer consists of a phase-controlled switching device bridge and the DC link consists of 1 or 2 series inductors between one or both legs of the connection between rectifier and inverter. Alternatively, an anti-parallel thyristor bridge must be provided in the rectifier section to feed energy back into the AC line. Such phase-controlled thyristor-based rectifiers however have higher AC line distortion and lower power factor at low load than diode-based rectifiers. PWM inverter to the DC-link.
The DC-link quantity is then impressed by an energy storage element that is common to both stages, which is a capacitor C for the voltage DC-link or an inductor L for the current DC-link. Due to the DC-link storage element, there is the advantage that both converter stages are to a large extent decoupled for control purposes. Furthermore, a constant, AC line independent input quantity exists for the PWM inverter stage, which results in high utilization of the converter’s power capability. On the other hand, the DC-link energy storage element has a relatively large physical volume, and when electrolytic capacitors are used, in the case of a voltage DC-link, there is potentially a reduced system lifetime. In order to achieve higher power density and reliability, it makes sense to consider Matrix Converters that achieve three-phase AC-AC conversion without any intermediate energy storage element. Kolar from the ETH Zurich. DC-link has no intermediate storage element.
Generally, by employing matrix converters, the storage element in the DC-link is eliminated at the cost of a larger number of semiconductors. Matrix converters are often seen as a future concept for variable speed drives technology, but despite intensive research over the decades they have until now only achieved low industrial penetration. However, citing recent availability of low-cost, high performance semiconductors, one larger drive manufacturer has over past few years been actively promoting matrix converters. Proceedings of the IPEC’90, Tokyo, Japan, , pp. Proceedings of the NORPIE’2000, Aalborg, Denmark, pp. Proceedings of the 32nd IEEE IECON’06, Paris, France, Nov. IEEE Transactions Industry Electronics, Vol.
Proceedings of the 36th IEEE IAS’01, Chicago, USA, vol. This page was last edited on 9 November 2017, at 21:09. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses. For shorter distances, the higher cost of DC conversion equipment compared to an AC system may still be justified, due to other benefits of direct current links. Since the power flow through an HVDC link can be controlled independently of the phase angle between source and load, it can stabilize a network against disturbances due to rapid changes in power. HVDC also allows transfer of power between grid systems running at different frequencies, such as 50 Hz and 60 Hz. This improves the stability and economy of each grid, by allowing exchange of power between incompatible networks.
12 GW of power, setting world records for highest voltage, longest distance and largest transmission capacity. Many of these HVDC lines in 2008 transfer power from renewable sources such as hydro and wind. For a given quantity of power transmitted, doubling the voltage will deliver the same power at only half the current. Since the power lost as heat in the wires is proportional to the wires’ resistance as a share of the total resistance, and doubling voltage allows for the quadrupling of non-transmission resistance without losing power, doubling the voltage reduces the line losses per unit of electrical power delivered by approximately a factor of 4. While power lost in transmission can also be reduced by increasing the conductor size, larger conductors are heavier and more expensive.
High voltage cannot readily be used for lighting or motors, so transmission-level voltages must be reduced for end-use equipment. This system transmitted 630 kW at 14 kV DC over a distance of 120 km. 8,600 kW of hydroelectric power a distance of 200 km, including 10 km of underground cable. This system used eight series-connected generators with dual commutators for a total voltage of 150,000 volts between the positive and negative poles, and operated from c.
Fifteen Thury systems were in operation by 1913. Other Thury systems operating at up to 100 kV DC worked into the 1930s, but the rotating machinery required high maintenance and had high energy loss. 20th century with little commercial success. German government in 1945 the project was never completed. The nominal justification for the project was that, during wartime, a buried cable would be less conspicuous as a bombing target. Sweden and the island of Gotland marked the beginning of the modern era of HVDC transmission.
Mercury arc valves require an external circuit to force the current to zero and thus turn off the valve. LCCs require rotating synchronous machines in the AC systems to which they are connected, making power transmission into a passive load impossible. Since then, all mercury arc systems have been either shut down or converted to use solid state devices. North and South Islands of New Zealand, which used them on one of its two poles. The mercury arc valves were decommissioned on 1 August 2012, ahead of commissioning of replacement thyristor converters. Like mercury arc valves, thyristors require connection to an external AC circuit in HVDC applications to turn them on and off. Development of thyristor valves for HVDC began in the late 1960s.