This paper proposes an input voltage sensorless control algorithm for three-phase active boost rectifiers. Using this approach, the input ac-phase voltages can be accurately estimated from the fluctuations of other measured state variables and preceding switching state information from converter dynamics. Furthermore, the proposed control strategy reduces the input current harmonics of an ac–dc three-phase boost power factor correction (PFC) converter by injecting an additional common-mode duty ratio term to the feedback controllers’ outputs. This additional duty compensation term cancels the unwanted input harmonics, caused by the floating potential between ac source neutral and dc link negative, without requiring any access to the neutral point. A 6-kW (continuous power)/10-kW (peak power) three-phase boost PFC prototype using SiC-based semiconductor switching devices is designed and developed to validate the proposed control algorithm. The experimental results show that an input power factor of 0.999 with a conversion efficiency of 98.3%, total harmonic distortion as low as 4%, and a tightly regulated dc-link voltage with 1% ripple can be achieved.

Input Voltage Sensorless Duty Compensation Control for a Three-Phase Boost PFC Converter

A system and method for reducing harmonics in a circuit is disclosed. The system comprises a main rectifier, ( n 3 - 1 ) 
auxiliary rectifiers connected to the main rectifier, and an autotransformer connected to both the main rectifier and the auxiliary rectifiers which provides 2n-pulse rectification where n equals the number of phases of the system. The autotransformer generates ( n 3 - 1 ) 
auxiliary voltage sets, each auxiliary voltage set having an auxiliary voltage amplitude, k, and an auxiliary voltage phase, α, wherein k = 4 + 2 ⁢ 3 ⁢ cos ⁢ ( θ - 7 ⁢ π 6 ) 
and wherein α = sin - 1 ⁢ ( 3 ⁢ sin ⁢ ⁢ θ - 0.5 k ) 
assuming a main voltage amplitude of one and a main voltage phase of ninety degrees, wherein θ = 180 ⁢ ° n 
and its integral multiples for all possible real values of k. The main rectifier has a main rectifier power rating, P mdb wherein P mdb ≥ ( n + 3 2 ⁢ n ) 
times the load power, and the auxiliary rectifiers each have an auxiliary power rating, P auxdb , wherein P auxdb ≤ ( 3 2 ⁢ n ) 
times the load power.

Autotransformer-based system and method of current harmonics reduction in a circuit

Transformer rectifier units (TRU) for the conversion of AC to regulated DC are disclosed. One aspect of a TRU according to the invention is output boost regulation by monitoring the output from a conventional TRU, and when the output drops below 28 volts DC an additional electronic switching converter boosts the output up to the 28 volt DC level. Under overload conditions a bypass diode returns the operation to that of a conventional TRU to maintain the required high current. Another aspect, input buck regulation, regulates by controlling the impedance of an auxiliary TRU by transferring its output to the DC output via a conventional flyback converter.

Means for transformer rectifier unit regulation

A power converter for converting three phase input power to DC output power and a method of effecting such conversion. The power converter includes: (1) three single phase DC converters, each having outputs, that receive the three phase input power, (2) a DC/DC converter coupled to the outputs of the three single phase DC converters and (3) a converter selection circuit, associated with the three single phase DC converters, that selects a selected subset of the three single phase DC converters as a function of an electrical characteristic of each phase of the three phase input power to conduct a portion of the three phase input power to the DC/DC converter, the converter selection circuit permitting the power converter to operate on the three phase power with less than three DC/DC converters.

Three phase rectifier using three single phase converters and a single DC/DC converter

A three-phase 48-pulse rectifier transformer consists of two 24-pulse rectifier transformers phase-shifted through valve-side output windings. Each 24-pulse rectifier transformer comprises two sets of grid-side input windings and four sets of valve-side output windings. The two sets of grid-side input windings are connected in parallel and axially arranged in a split manner. Among the four sets of valve-side output windings, two sets of valve-side output windings are radially arranged in a split manner corresponding to one set of grid-side input windings, and the other two sets of valve-side output windings are also radially arranged in a split manner corresponding to the other set of grid-side input windings. The two sets of valve-side output windings that are radially split and the other two sets of valve-side output windings that are radially split are axially arranged in a split manner. The grid-side input windings of the two 24-pulse rectifier transformers are phase-shifted with respect to each other. In this way, a uniform difference of 7.5° is produced in voltages of the eight sets of valve-side output windings of the two 24-pulse rectifier transformers, and the eight sets of valve-side output windings of the two 24-pulse rectifier transformers are correspondingly connected to rectifiers to form a uniform 48-pulse rectifier transformer, which not only reduces the harmonic current generated by the rectifier, but also improves the load capacity of the rectifier.

Three-phase 48-pulse rectifier transformer

A transformer rectifier unit is provided for developing regulated DC output power from first and second sources of unregulated DC power. The transformer rectifier unit includes a transformer having a primary winding connectable to a source of AC input power and first and second secondary windings. The first secondary winding develops AC power at a first level and the second secondary winding develops AC power at a second level lower than the first level. First and second rectifier circuits are respectively coupled to the first and second secondary circuits for rectifying the AC power therefrom to DC power having corresponding first and second DC levels. A switch is coupled between an output of the first rectifier circuit and an output of the second rectifier circuit and is operable in first and second switching states to provide DC output power from one of the rectifier circuits to a load. A pulse-width modulation control circuit is responsive to the difference between a desired DC output level and an actual DC output level and operates the switch between first and second states to provide regulated DC output power. In an alternative embodiment of the invention, the transformer comprises Y-Δ secondary winding sets.

Regulated transformer rectifier unit

A power supply (100) for producing a regulated output DC voltage from an AC voltage source (12) having at least one phase (14); a fullwave rectifier (16) coupled to the AC voltage source for producing a rectified output voltage potential, the fullwave rectifier having a number of pairs of diodes (D1-D6) equal to a number of phases of the AC voltage source; a number of pairs of magnetic amplifiers S1-S6 equal to a number of phases of the AC voltage source, each magnetic amplifier having a control input for varying an impedance between an input and an output in response to variation of a control signal; a control (36), responsive to the output voltage, for producing the control signal in response to the output voltage to cancel any variation in the output voltage from a regulated voltage; a fault detection circuit, responsive to an electrical load drawing current from the power supply for producing a shutdown signal; and a circuit, coupled to one of the magnetic amplifiers of each of the phases, responsive to the shutdown signal, for conducting current to the AC voltage source in response to the shutdown signal.

Robert A. Barnet

Papers

Regulated transformer rectifier unit

Magnetic amplifier shutdown circuit