Power converter control plays a crucial role in optimizing the overall performance of a power conversion system. With proper control, the efficiency of the power converter can be maximized, energy loss reduced and component life extended. By designing a complex control algorithm, the power conversion can be effectively and optimally managed while keeping the output voltage and current of the power converter constant.
An important aspect of power converter control is the ability to adapt to dynamic changes in load conditions and power supply characteristics. This allows the power converter to provide a stable and consistent output, regardless of changing power demand or environmental conditions. In addition, power converter control can include many functions such as output waveform adjustment, harmonic distortion compensation, and power quality management. These features enable it to adapt to the specific needs of the application and ensure a reliable, high-quality power supply.
Research and development in the field of power converter control is constantly leading to new technologies and more complex algorithms. The use of advanced digital controllers, combined with intelligent control algorithms based on machine learning, is opening up new perspectives for further improving the performance of power electronic converters. Pulse width modulation (PWM) technology is widely used to control power converters. This control method involves generating a signal that manages to turn the electronic switch of the power converter on and off to achieve the desired voltage value at the output end. This switching function (see the example in Figure 1) is achieved by comparing two signals: the modulated signal and the carrier. These two signals can be summarized as follows:
The modulated amount is a signal that contains actual information about the desired output voltage.
The carrier is a periodic signal, usually in the shape of a triangular wave, whose switching frequency corresponds to the switching frequency of the power converter.
Through the interaction of these two signals, a switching function is generated. As a demonstration, the system depicted in the figure consists of three types of generators, some real and some calculated and processed:
(1) Is a triangular signal, called the "carrier". It is a periodic and usually fixed frequency signal. Its form may vary depending on the need.
(2) Is the threshold voltage, called the "modulation" (or reference voltage). It determines the switching threshold level for the output logical state. It can be selected by the user, or it can be any waveform, such as a sine wave when running as an inverter.
(3) Is the switching voltage, which is the result of the intersection and comparison of the first two signals. It's called a binary switch function. In general, if the amount of modulation is greater than the carrier, the value is 1. Otherwise, its value is 0. This can be done through hardware (with a fast comparison circuit) or through firmware (by using a powerful microcontroller)
Figure 1: The switching function uses two types of signals
The results of the switching function are sent directly to the driver, which manages the switching of the power converter switch on and off according to the order of the 1 and 0 of the switching function. Thus, it can be seen that the result is a real PWM signal due to the presence of two different and easily controlled signals. The basic principle of PWM is to proportionally change the pulse width of the switching signal according to the required reference voltage. In this way, the effective output value of the power converter can be controlled to ensure proper regulation and high quality of the power signal. The use of PWM as implemented above offers many advantages, including high energy efficiency, improved output signal quality, the ability to control output power, and reduced power losses.
Figure 2: The duty cycle of the switching signal linearly follows the level of the modulated signal
In inverter design, technology is used to generate pure sine waves. Figure 3 shows the comparison of the carrier signal, the modulated signal, and the first two. It is worth noting that the output signal will inevitably be affected by the harmonics of the carrier and modulated signal. In order to reduce EMI effects, it is necessary to design filters to eliminate or reduce such undesirable factors as much as possible.
Figure 3: Sine wave modulation is widely used in inverter design
The generation of PWM signal with carrier and modulated signal is the basic technology of controlling power converter. The generation of switching functions can regulate the output voltage, thus providing accurate and efficient control of electronic converters. Understanding the fundamentals and applications of this technology is critical for engineers and power to help develop innovative solutions for controlling and optimizing power conversion.
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