The Vienna Rectifier is a pulse-width modulation rectifier, invented in 1993 by Johann W. Kolar at TU Wien, a public research university in Vienna, Austria. [1] [2]
The Vienna Rectifier provides the following features:
The Vienna Rectifier is a unidirectional three-phase three-switch three-level Pulse-width modulation (PWM) rectifier. It can be seen as a three-phase diode bridge with an integrated boost converter. [9]
The Vienna Rectifier is useful wherever six-switch converters are used for achieving sinusoidal mains current and controlled output voltage, when no energy feedback from the load into the mains is available. In practice, use of the Vienna Rectifier is advantageous when space is at a sufficient premium to justify the additional hardware cost. These include:
Figure 2 shows the top and bottom views of an air-cooled 10 kW-Vienna Rectifier (400 kHz PWM), with sinusoidal input current s and controlled output voltage. Dimensions are 250mm x 120mm x 40mm, resulting in a power density of 8.5 kW/dm3. The total weight of the converter is 2.1 kg [10]
Figure 3 shows the system behaviour, calculated using the power-electronics circuit simulator. [11] Between the output voltage midpoint (0) and the mains midpoint (M) the common mode voltage u0M appears, as is characteristic in three-phase converter systems.
It is possible to separately control the input current shape in each branch of the diode bridge by inserting a bidirectional switch into the node, as shown in Figure 3. The switch Ta controls the current by controlling the magnetization of the inductor. When the bi-directional switch is turned on, the input voltage is applied across the inductor and the current in the inductor rises linearly. Turning off the switch causes the voltage across the inductor to reverse and the current to flow through the freewheeling diodes Da+ and Da-, decreasing linearly. By controlling the switch on-time, the topology is able to control the current in phase with the mains voltage, presenting a resistive load behavior (Power-factor correction capability).
To generate a sinusoidal power input which is in phase with the voltage the average voltage space vector over a pulse-period must satisfy: For high switching frequencies or low inductivities we require () . The available voltage space vectors required for the input voltage are defined by the switching states and the direction of the phase currents. For example, for , i.e. for the phase-range of the period() the phase of the input current space vector is ). Fig. 4 shows the conduction states of the system, and from this we get the input space vectors shows in Fig. 5 [12]
In electrical engineering, the power factor of an AC power system is defined as the ratio of the real power absorbed by the load to the apparent power flowing in the circuit. Real power is the average of the instantaneous product of voltage and current and represents the capacity of the electricity for performing work. Apparent power is the product of root mean square (RMS) current and voltage. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power may be greater than the real power, so more current flows in the circuit than would be required to transfer real power alone. A power factor magnitude of less than one indicates the voltage and current are not in phase, reducing the average product of the two. A negative power factor occurs when the device generates real power, which then flows back towards the source.
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