Reprinted from http://www.elecfans.com/dianzichangshi/20180515677376.html
pwm with spwm has been widely used, but many people do not quite understand the difference between them, this paper describes is the difference between pwm and spwm, the second section describes the principles and advantages of PWM, and finally describes what spwm principle, specific follow Xiaobian a look at it.
First, the difference between the PWM and SPWM
A difference
English is PWM Pulse Width ModulaTIon (pulse width modulation) Abbreviation, according to certain rules changing the pulse width of the pulse sequence, one modulation mode to regulate the output and waveform.
English PAM Pulse Amplitude ModulaTIon (pulse amplitude modulation) Abbreviations, according to certain rules to change the pulse amplitude of the pulse sequence, one modulation mode to regulate the output and waveform.
Difference between the two
PWM is pulse width modulated square wave having a continuous constant pulse width composition.
SPWM is based on a sine wave PWM modulated square wave having a sine wave synthesis law changes.
Sine wave PWM signal SPWM principle of a sine wave, the sine wave is equivalent to a series of amplitude equal width rectangular pulse waveform is a sine wave pulse width and intersects the triangular wave generated naturally.
There are many ways of generating a sinusoidal waveform, but more typically are: symmetry regular sampling, and a mean asymmetry rule sampling symmetry regular sampling three.
Since the first method of generating PWM pulse width is small, the output voltage of the inverter DC voltage is less than twice;
In a second method to be sampled twice carrier cycle sine wave, the output voltage is clearly higher than the former, but for the microprocessor, the increased amount of data processing when the carrier frequency is higher, the higher the requirements of the microcomputer;
The third method most widely used, which take into account the advantages of the first two methods.
Two, PWM
About PWM
The PWM, i.e. Pulse Width Modulation, in English "Pulse the Width Modula TI ON" acronym, or pulse width modulation, the microprocessor uses the digital output of the analog circuit to control a very effective technique, widely used in the measurement, communications to many areas of the power control and conversion.
PWM principle
With the development of electronic technology, a variety of PWM technology, which comprises: a voltage controlled phase PWM, pulse width PWM method, random PWM, of SPWM method, a line voltage control PWM, etc., while the use of the nickel-hydrogen battery smart charger method PWM pulse width, which is equal to the average width of each pulse as a pulse train of the PWM waveform can be frequency modulated by changing the period of the pulse train, changing the width or the duty cycle of the pulses may regulator, a control method appropriate to the voltage coordination of the change of frequency. By adjusting the PWM cycle, the PWM duty cycle to control the charging current object.
Value of the analog signal can be varied continuously, time and magnitude of the resolution in both. 9V battery is a kind of analog devices, because its output voltage is not exactly equal to 9V, but varies with time, and can take any real value. Similarly, a current from the battery is not within a defined set of possible values. The difference between analog and digital signals is that the latter values only from a set of possible values within the pre-determined, in this example, the value set {0V, 5V} in.
Analog voltages and currents can be used for controlling, such as controlling the volume of the car radio. In a simple analog radio, a knob is connected to a variable resistor. While tightening the knob, the resistance value becomes larger or smaller; current flowing through the resistor also increases or decreases, thereby changing the current driving the speakers, sound volume becomes correspondingly larger or smaller. Like the radio, the analog output circuit is linearly proportional to the input.
Although analog control may seem intuitive and simple, but it is not always economically attractive or feasible. For one thing, the analog circuitry is easy to drift over time, making it difficult to adjust. Precision analog circuits can solve this problem may be very large, heavy (such as older home stereo equipment), and expensive. Analog circuits can also get very hot, the power dissipated is proportional to the product of the voltage across the current working element. Analog circuitry may be very sensitive to noise, or any noise disturbance necessarily changes the magnitude of the current value.
By digitally controlling an analog circuit, it can significantly reduce the cost and power consumption. In addition, many DSP and microcontroller already contains a PWM controller on the chip, which makes the digital control becomes easier.
PWM advantage
One advantage is the PWM signal from the processor to the controlled system is in digital form, without the need for digital to analog conversion. By keeping the signal in digital form may be noise to a minimum. Only noise is strong enough to change when a logic 1 or a logic 0 to a logic 0 to a logic 1, can also have an impact on the digital signal.
Increased noise immunity is yet a further advantage with respect to the analog PWM control, and this is sometimes the reason PWM communications. Switching from an analog PWM signal can greatly extend the communication distance. At the receiving end, a suitable RC or LC network can remove the high frequency square wave and a modulation signal into analog form.
In short, PWM is economical, space-saving, anti-noise performance is an effective technique worthy of the majority of design engineers for use in many applications.
Three, SPWM
SPWM Profile
PWM stands for Modula the Width Pulse TI ON (pulse width modulation), which is equivalent to the output voltage to change by changing the duty cycle of the output square wave. And widely used in the motor speed control valves, such as an electric vehicle motor control is used in this way.
Of SPWM called, is changed on the basis of the PWM modulation on the pulse, the duty ratio of the pulse width time sinusoidally arranged, so that the output waveform can be done appropriately filtered sine wave output. It is widely used for DC-AC inverter, etc., such as advanced is an example of some of the UPS. Three-phase SPWM SPWM output is an analog three-phase mains, has been widely adopted in the area of the drive.
SPWM principle
Sine wave PWM signal is a sine wave, the sine wave is equivalent to a series of amplitude equal width rectangular pulse waveform is a sine wave pulse width and intersects the triangular wave generated naturally. There are many ways of generating a sinusoidal waveform, but more typically are: symmetry regular sampling, and a mean asymmetry rule sampling symmetry regular sampling three. Since the first method of generating PWM pulse width is small, the output voltage of the inverter is less than twice the DC voltage; a second method to be sampled twice carrier cycle sine wave, the output voltage is higher than the former apparently , but for the microprocessor, the increased amount of data processing when the carrier frequency is higher, the higher requirement for the microcomputer; third method most widely used, which take into account the advantages of the first two methods. Although SPWM three-phase sinusoidal voltage can be obtained, but lower DC side voltage utilization rate, times the maximum DC voltage side, which is the largest drawback of this method.