Rectifier circuit and its classification

Rectifier circuit and its classification

Overview

A Rectifying Circuit is a circuit that converts AC electrical energy into DC electrical energy. Usually the rectifier circuit is composed of AC power supply (power frequency grid or rectifier transformer), rectifier main circuit, filter, load and trigger control circuit. It is widely used in DC motor speed regulation, generator excitation regulation, electrolysis, electroplating and other fields. After the 1970s, the main circuit is mostly composed of silicon rectifier diodes and thyristors, and the filter is connected between the main circuit and the load to filter out the AC component in the pulsating DC voltage. Whether the rectifier transformer is set or not depends on the specific situation. The function of the rectifier transformer is to achieve the matching between the AC input voltage and the rectified output DC voltage and the electrical isolation between the AC grid and the rectifier circuit.

Classification of rectifier circuits

(1) Classification according to the devices that make up the rectifier circuit

1) Uncontrollable circuit rectifier circuit; it is composed of uncontrollable rectifier diodes. After the circuit structure is determined, the ratio of the average value of the rectified output DC voltage to the AC power supply voltage value is fixed.

2) Semi-controlled rectifier circuit: It is composed of a mixture of controllable elements and diodes. In this circuit, the polarity of the load voltage cannot be changed, but the average value can be adjusted.

3) Fully controlled rectifier circuit: All rectifier elements are controllable (SCR, GTR, GTO, etc.), and the average value and polarity of the output DC voltage can be adjusted by controlling the conduction state of the element. In this kind of circuit, the power can either be transmitted from the power source to the load, or fed back to the power source by the load, that is, the so-called active inverter.

(2) Classification by circuit structure

1) Zero-type rectifier circuit: refers to a circuit with a zero or neutral point, also known as a half-wave circuit. Its characteristic is that the cathodes (or anodes) of all rectifier elements are connected to a common contact to supply power to the DC load, and the other line of the load is connected to the zero point of the AC power supply.

2) Bridge rectifier circuit: It is actually composed of two half-wave circuits in series, so it is also called a full-wave rectifier circuit.

(3) Classification according to the number of AC input phases

1) Single-phase rectifier circuit: Single-phase power supply is often used for low-power rectifiers. Single-phase rectifier circuits are divided into half-wave rectifier circuits, full-wave rectifier circuits, bridge rectifier circuits and voltage doubler rectifier circuits.

2) Three-phase rectifier circuit: The AC side is powered by a three-phase power supply, which is mainly used in situations where the load capacity is large or the DC voltage pulsation is required to be small. The three-phase controllable rectifier circuit includes a three-phase half-wave controlled rectifier circuit, a three-phase half-controlled bridge rectifier circuit and a three-phase fully-controlled bridge rectifier circuit. Because the three phases of the three-phase rectifier are balanced, the output DC voltage and current ripple are small, the influence on the power grid is small, and the control lag time is short, when using a three-phase fully-controlled bridge rectifier circuit, the lowest frequency of the alternating component of the output voltage is 6 times the frequency of the grid, and the ratio of the alternating component to the direct current component is also small. Therefore, the inductance of the filter is much smaller than that of the single-phase or three-phase half-wave circuit of the same capacity. In addition, the voltage rating of the thyristor is also lower. Therefore, this circuit is suitable for high-power converter devices.

3) Multi-phase rectifier circuit: as the power of the rectifier circuit further increases (for example, the power of the rolling steel motor reaches several megawatts), in order to reduce the interference to the power grid, especially the impact of high-order harmonics of the rectifier circuit on the power grid, twelve-phase, eighteen-phase, twenty-four-phase, and even thirty-six-phase multi-phase rectifier circuits can be used. Using a multi-phase rectifier circuit can improve the power factor, increase the pulsating frequency, and make the waveform of the primary current of the transformer closer to a sine wave, thereby significantly reducing the influence of harmonics. Theoretically, as the number of phases increases, the influence of harmonics can be further attenuated. Multi-phase rectifier circuits are commonly used in the field of high-power rectifiers, and the most commonly used are double-inverse star neutral point with balanced reactor connection and three-phase bridge connection.

(4) Classification by control method

1) Phase-controlled circuit: The method of controlling the magnitude of the rectified output DC voltage by controlling the phase of the trigger pulse is called the phase control method, or phase-controlled mode for short.

2) Chopper circuit (chopper): use thyristor and self-shutoff device to realize on-off control, add the DC power supply voltage to the load intermittently, and change the average value of the load voltage through the change of on and off time. Also known as DC-DC converter. It has the advantages of high efficiency, small size, light weight and low cost, and is widely used in variable-speed traction of DC traction, such as urban trams, subways, battery cars, etc.

(5) According to the different classification of lead-out methods

1) According to the neutral point, the rectifier circuit is divided into: single-pulse (single-phase half-wave), two-pulse (single-phase full-wave), three-pulse (three-phase half-wave), and six-pulse (six-phase half-wave).

2) According to the bridge rectifier circuit: two-pulse (single-phase) bridge, six-pulse (three-phase) bridge.

3) According to the rectifier circuit with balanced reactor: the primary side star-connected six-pulse band balanced reactor circuit (that is, the double-reverse star-shaped balanced reactor circuit), the primary side delta-connected six-pulse band balanced reactor circuit.

4) According to twelve-phase rectifier circuit: secondary side star, delta connection, bridge parallel single unit twelve-pulse rectifier circuit; secondary side star, delta connection, bridge series twelve-pulse rectifier circuit; twelve-pulse rectifier circuits such as bridge-type parallel connection; twelve-pulse rectifier circuits such as double-reverse star with balanced reactor.