Basic principle of PWM control (Pulse Width Modulation)

The control method is to control the on-off of the switching device of the inverter circuit, so that a series of pulses of equal amplitude are obtained at the output, and these pulses are used to replace the sinusoidal waveform or the desired waveform, that is, multiple pulses are generated in half a cycle of the output waveform, so that the equivalent voltage of the pulses is a sinusoidal waveform, and the obtained output is smooth and with fewer low harmonics, and the widths of the pulses are modulated according to a certain rule, which can both Modulating the width of each pulse according to certain rules can change both the size of the output voltage and the output frequency of the inverter circuit.

Introduction of Pulse Width Modulation

Pulse width modulation is a kind of analog control method, which modulates the bias of transistor base or MOS gate according to the change of the corresponding load to realize the change of transistor or MOS on-time, thus realizing the change of switching regulator power supply output, which can make the power supply's output voltage remain constant when the working conditions change, and it is a very effective technique to control the analog circuit by using microprocessor's digital signal. Pulse width modulation is a very effective technique for controlling analog circuits using the digital output of a microprocessor, and is widely used in many fields ranging from measurement and communication to power control and conversion.

Background of Pulse Width Modulation

With the development of electronic technology, a variety of pulse width modulation techniques have appeared, including: phase voltage control PWM, pulse width PWM method, random PWM, SPWM method, line voltage control PWM, etc., and the pulse width PWM method used in the nickel-metal hydride battery smart charger, which uses a pulse train with each pulse of equal width as a PWM waveform, and can be used to modulate the frequency by changing the period of the pulse train, and changing the By changing the period of the pulse train, the frequency can be regulated, and by changing the width or duty cycle of the pulse, the voltage can be regulated, and the voltage can be coordinated with the frequency by using the appropriate control method, and the purpose of controlling the charging current can be achieved by adjusting the period of the PWM and the duty cycle of the PWM.

Characteristics of Pulse Width Modulation

PWM is characterized by the signal from the processor to the controlled system are in digital form, without the need for digital-to-analog conversion, so that the signal remains in digital form can minimize the impact of noise, noise is only strong enough to change the logic 1 to logic 0 or logic 0 to logic 1, but also to have an impact on the digital signal.

Increased resistance to noise is another advantage of PWM over analog control, and it is the main reason why PWM is used in communications at some point. Switching from analog to PWM can greatly extend the communication distance, and at the receiving end, an appropriate RC or LC network can filter out the modulating high-frequency square waves and return the signal to analog form.

Control Methods

Equal pulse width PWM method

Equal pulse width PWM method is one of the simplest PWM method, it is the width of each pulse is equal to the pulse train as a PWM wave, by changing its period, to achieve the effect of frequency modulation, change the width of the pulse or duty cycle can be regulated by the voltage, the use of appropriate control methods can be coordinated to make the voltage and frequency changes.

Random PWM

Beginning in the 1970s to the early 1980s, due to the then high-power transistors are mainly bipolar Darlington transistor, the carrier frequency is generally not more than 5kHz, the electromagnetic noise of the motor winding and the vibration caused by harmonic caused by people's concern, in order to improve, random PWM method came into being.

SPWM method

SPWM method is a more mature, now more widely used PWM method, mentioned earlier in the sampling control theory of an important conclusion: the impulse is equal but different shapes of narrow pulse added to the link with inertia, the effect is basically the same.

Line voltage control PWM

The various PWM control methods described above for three-phase inverter circuit, are the three-phase output phase voltage control, so that the output is close to sinusoidal, but for three-phase asynchronous motor such as three-phase symmetrical loads without a center line, the inverter output does not have to pursue the phase voltage is close to sinusoidal, but can be geared to make the line voltage tends to be sinusoidal.

Current-controlled PWM

The basic idea of current control PWM is to take the desired current waveform as the command signal and the actual current waveform as the feedback signal, and decide the on/off of each switching device by comparing the instantaneous values of the two, so that the actual output changes with the command signal.

Applications

Telecommunications

In telecommunication, pulse width modulation is a form of signal modulation in which the width of a pulse wave corresponding to a specific information is encoded at the transmitting end and decoded at the receiving end, and pulse waves of different lengths are transmitted at fixed intervals.

Transmission of Energy

Pulse Width Modulation (PWM) can be used to control how much energy is transferred to a carrier without incurring the linear energy transfer losses caused by impedance, at the cost that the energy lost by the carrier is not constant and is not continuous, nor is the energy transferred to the carrier continuous.

PWM signal (Pulse Width Modulation) is a special form of signal that is widely used in many aspects of electronics. The following is a detailed analysis of the PWM signal, aiming to discuss its meaning, characteristics, applications and future development trends.

PWM, full name is Pulse Width Modulation, that is, pulse width modulation. It is a method of controlling or simulating a signal by changing the width (duty cycle) of the pulse signal. In a PWM signal, each pulse consists of a high level and a low level, and the ratio of the width of the pulse (i.e., the duration of the high level) to the entire period is called the duty cycle. By adjusting the duty cycle, the PWM signal enables approximate or precise control of an analog signal.

The operation of PWM signals is based on a simple idea: control the average voltage or current in a circuit by varying the width of the pulse. Specifically, the PWM signal generator adjusts the duty cycle of the output PWM waveform according to the input control signal (e.g., analog or digital). When the PWM signal acts on the components in the circuit (e.g., motor, LED, etc.), its average voltage or current will change with the pulse width, thus realizing the control of the circuit.

In summary, as an important signal control technology, PWM signal plays a pivotal role in the field of electronics. Through continuous exploration and innovation, the application fields and realization methods of PWM signals will be further expanded and improved to provide strong support for the intelligence, efficiency and reliability of modern electronic systems.