Inverter Pulse Width Modulation Technology
Author: Source: Datetime: 2016-09-30 10:18:11
The basic principle: fixed inverter operating frequency, adjust the time ratio of switching tube δ, thus adjusting the output (supply voltage and current load) size, in order to stabilize the output. Δ is the switching duty cycle, for single-ended power conversion circuit, δ ≤ 0.5, which is equal to the duty cycle of power transmission; for double-ended power conversion circuit, which is equal to the power transfer duty cycle half. The maximum duty cycle of the power transfer can be approximately equal to one.
PMW transformation characteristics and applications: Transform can be used for almost all of the inverter main circuit topology. Such as single-ended, push-pull, half-bridge, full-bridge, step-down, step-up, isolated, non-isolated, single-phase, three-phase passive, active, square, sine Wave inverter main circuit can be used.
Sine wave technology
Sine-wave PWM technology, known as SPWM technology, the use of more common, single-phase SPWM technology is relatively simple, it generally has two forms. Unipolar SPWM waveform: unidirectional sine wave into a unipolar, and unipolar symmetrical triangular wave comparison obtained after the pulse sequence, and then inverted with the inverted signal. Bipolar SPWM waveform: direct sine wave and bipolar symmetrical triangular wave can be compared bipolar SPWM waveform.Different wave use different solar power generations.
With the development of large scale integrated circuit manufacturing technology, integrated SPWM chip with perfect overvoltage, overcurrent, undervoltage protection circuit and program control, remote control and synchronous operation function has been produced, which is composed of SPWM chip Of the micro-inverter can be installed directly on the back of the PV module can be issued by the photovoltaic module directly into the standard sine wave AC power connected to the grid.No matter what kind of photovoltaic systems, need inverters, especially solar powered portable generator, the inverter requirements are higher
Basic Characteristics and Evaluation of Inverter
- Output waveform: square wave inverter Advantages: simple circuit, low cost; shortcomings of high harmonics, voltage adjustment range is small, with inductive load efficiency is low, electromagnetic interference, the use of electrical appliances have adverse effects.
- Sine wave inverter: In the independent photovoltaic system requires less than 5% distortion, which is ideal for the inverter, compared to the more complex lines, the cost is higher.
- Output frequency: There are frequency (50Hz) and VHF and other high frequency, frequency increases can greatly reduce the size of the transformer, reducing copper loss and iron loss, improved efficiency and increased reliability.
- DC / AC conversion efficiency: the efficiency of the inverter is usually between 70% -90%, high-quality inverter can reach 90% -96%, it should be noted that the efficiency of the inverter often changes with the load rate .
- Operating temperature: a direct impact on the inverter output voltage, waveform, frequency, phase and other parameters. The operating temperature and the ambient temperature, geographical altitude, humidity and working conditions. When the inverter is to be used in very hot and cold areas, the operating temperature must be pre-designed.
- Working environment: For high-frequency small inverter, its working characteristics and the environment and work status. In the high altitude areas, due to the thin air, prone to inter-circuit discharge of the impact of work in high humidity areas, prone to condensation due to local short-circuit, and therefore for each inverter, must specify the applicable working environment.
- Electromagnetic interference and noise: Inverter switch circuit easy to produce electromagnetic interference, transformer core is easy to have noise, so in the design and manufacturing process must be strictly controlled.
- Overload capacity: In some television sets, motors and other load starts, the instantaneous power can work for the power of 3-6 times, which requires the inverter has instantaneous overload capacity, also known as the peak coefficient. In addition, under special circumstances, there will be some additional load increases, but also requires a certain inverter overload capacity.
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