The control methods for various conversion circuits can be summarized into the following three types:
(1) Phase control mode: refers to the change of the amplitude of the control signal being converted into a change of the phase of the trigger pulse of the converter device. This control mode is commonly used in rectifier power supplies or AC regulated power supplies.
(2) Frequency control method: This refers to the change in the amplitude of the control signal being converted into a change in the frequency of the trigger pulse of the converter device. This control method is commonly used in inverter power supplies.
(3) Chopper control mode: refers to the change of the control signal amplitude being converted into a change of the “conduction time ratio” of the converter device. This control mode is commonly used in DC-DC converter circuits.
The three control methods mentioned above can also be used in combination. For example, when chopping and frequency control are used simultaneously, they constitute a sine wave pulse width modulation (SPWM) method, which is commonly used in AC converters.
3. Composition of the power supply system
A typical power supply system consists of power supplied by mains electricity (grid), batteries, solar energy, or a fuel generator. A rectifier converts the alternating current (AC) from the mains or generator into direct current (DC), or converts the DC from the battery into DC of another voltage level, which is then sent to a DC distribution panel. The AC from the mains or generator is then sent to an AC distribution panel via a voltage regulator. To improve power supply reliability, an uninterruptible power supply (UPS) is included in the system. When the mains power is interrupted, its energy is supplied by batteries or a fuel generator, and its output is sent to the AC distribution panel. For safe power supply, a lightning protection device is installed, which protects the rectifier, AC voltage regulator, UPS, and generator. In the diagram, the rectifier, UPS, and solar energy can all charge the batteries.
This system diagram clearly illustrates the relationships between various devices. Of course, to further improve power supply reliability, backup equipment, intelligent monitoring, and alarm displays can be added. Power supply technology has a significant promoting effect on science and technology, as well as industrial and agricultural production, and countries around the world attach great importance to its development. my country’s power supply technology has kept pace with international advanced levels and has made significant progress in the past 20 years. The overall development trend is:
(1) Power semiconductor devices: The focus is on developing fully controlled power devices. Currently, devices such as power MOSFETs and 1GBTs are developing rapidly because these devices have self-turn-off capability, which can eliminate the commutation circuit used in the original semi-controlled devices. This has the advantages of simplifying the circuit, improving reliability, increasing efficiency, and reducing cost. At the same time, it can also increase the switching frequency, achieve further reduction in size and weight, improve output waveform, and reduce noise. Power semiconductor devices continue to develop towards increasing capacity, improving dynamic performance, and moving towards modular and combined types.
(2) Power conversion circuit: Currently, fully controlled devices and pulse width modulation (PWM) are widely used, and source-side power factor correction (PFC) circuit is adopted to make the input current sinusoidal, thereby saving power and reducing interference to the power grid, overcoming the disadvantage of low input power factor of phase control mode.
The currently popular resonant soft-switching and other new circuits have enabled the operating frequency of switching power supplies to increase from the hundreds of kilohertz to the megahertz level, further improving efficiency, miniaturizing power supply equipment, and significantly reducing ripple voltage, thereby improving power supply performance. From the perspective of control methods, the hardware circuits composed of discrete components and small- and medium-scale integrated circuits have evolved into software control methods composed of microprocessors and single-chip microcomputers, thus achieving a higher degree of digitalization and intelligence, and further improving the reliability of power supply equipment. As can be seen from the above, power supply technology is developing rapidly and will make a greater contribution to production and scientific and technological progress.