This article mainly introduces the relevant introduction about the triangular wave carrier, and focuses on the detailed explanation of the role of the triangular wave carrier in the principle of spwm. SPWM (Sinusoidal PWM) method is a relatively mature method, and the PWM method is widely used at present. An important conclusion in the sampling control theory mentioned earlier: when narrow pulses with the same impulse and different shapes are applied to a link with inertia, the effect is basically the same. The SPWM method is based on this conclusion. The pulse width changes according to the sine law and the PWM waveform equivalent to the sine wave, that is, the SPWM waveform controls the on and off of the switching devices in the inverter circuit, so that the area of ​​the output pulse voltage is the same as that of the sine wave. It is hoped that the output sine wave has the same area in the corresponding interval, and the frequency and amplitude of the output voltage of the inverter circuit can be adjusted by changing the frequency and amplitude of the modulating wave. Pulse width modulation technology uses a certain rule to control the on and off of switching elements to obtain a set of rectangular pulse waveforms of equal amplitude but not equal width to approximate the sinusoidal voltage waveform. The application of pulse width modulation technology in inverters has greatly promoted the development of modern power electronics technology and modern speed control systems. In recent years, due to the continuous emergence of field-controlled self-shutdown devices, the corresponding high-frequency SPWM (sine pulse width modulation) technology has been widely used in motor speed regulation. SA8281 is an integrated circuit for three-phase SPWM wave generation and control launched by MITEL. It is convenient to interface with a microprocessor. It has a built-in waveform ROM and corresponding control logic. After the setting is completed, three-phase PWM waveforms can be generated independently. When the output frequency or amplitude needs to be changed, the intervention of the microprocessor is needed. The microprocessor only needs a little time to control it, so it has the ability to perform the inspection of the entire system. Protection and control, etc. The inverters based on SA8281 and 89C52 have simple circuits. full functioning. High performance-price ratio. Good reliability and other advantages. The triangular wave carrier acts as the carrier in the SPWM. This triangular wave is an isosceles triangular wave, because the horizontal width and height of any point on the isosceles triangular wave are linear and symmetrical. When it intersects any gently changing modulation signal wave, if it is at the intersection point By controlling the on and off of the switching devices in the circuit at all times, a pulse whose width is proportional to the amplitude of the signal wave can be obtained. When the modulating signal wave is a sine wave, what is obtained is the SPWM wave. Why SPWM adopts the triangular wave carrier SPWM? That is, the modulation pulse mode is changed on the basis of PWM, and the pulse width time duty ratio is arranged according to the sinusoidal rule, so that the output waveform passes Proper filtering can achieve sine wave output. It is widely used in DC and AC inverters, and more advanced UPS is an example. Three-phase SPWM is the use of SPWM to simulate the three-phase output of the mains, which is widely used in the field of inverters. The full name of PWM is PulseWidthModulation (pulse width modulation), which changes the equivalent output voltage by changing the duty cycle of the output square wave. It is widely used in motor speed control and valve control. For example, our current electric vehicle motor speed control uses this method. Generally speaking, the calculated duty cycle is a piece of data. You need to refer to it if you want to convert this data into time. For example, in simulation, the cycle of the triangle wave is synchronized with the simulation time, so you can get the result by comparing the duty cycle data with the triangle wave. Switching time. In DPS program control, this triangle wave is equivalent to the two-way counting mode of the timer. The triangular wave acts as a linear time reference, converting the calculated amount of time into actual time. The reason for using the triangle wave as a reference is that the 5-segment method and the 7-segment method are generally used for vector synthesis, and the switching action in one cycle is symmetric. If you use the 4-segment method, you cannot use the triangle wave. 1. SPWM technology is to hope that the output voltage waveform is a sine wave, and the average voltage is adjusted by adjusting the duty cycle. 2. Triangle wave as carrier wave (set period register of epwm) Sine wave as modulating wave 3. Principle: The DSP timer generates a triangular wave for counting up and down, and there is no negative half wave, so the coordinate far point is set at the trough of the triangular wave to obtain a bipolar SPWM Assumption: The amplitude of the triangular wave carrier is Ur/2, the period is Tr, the frequency is fr, and the amplitude of the sine wave is Us 1) Get the sine wave function: us=Us*sin(wts) 2) Carrier ratio N=fs/fr 3) Modulation degree M=Us/(Ur/2) (0= 4) According to the geometric relationship, Ton/(Tr/2)=(0.5Ur+Us*sin(wts))/Ur Because Us=M*Ur/2 So Ton=(Tr/4)(1+Msin(wts)) Where ts is the sampling time, wts=k*2π/N, ke0,1,2,3,4,5,6,……,N-1, 5) The value of the sine wave function at the sampling time can be made into a data table and stored in the DSP for query. Since the trigonometric function has symmetry, it is enough to store the sine function value of the half-period value into the DSP, and the other half-period can be obtained by conversion. Phase B and Phase C can be moved by 120°, 240°. (Sine wave lags behind, carrier does not need to lag (TBPRD)) That's it for the related introduction of triangle wave carrier. I hope this article can be helpful to you. Shenzhen Kate Technology Co., Ltd. , https://www.katevape.com
The main idea of ​​SVPWM is to use the three-phase symmetrical sine wave voltage power supply as the reference standard for the ideal flux circle of the three-phase symmetrical motor stator, and appropriately switch the different switching modes of the three-phase inverter to form a PWM wave. The actual flux linkage vector is used to track its accurate flux linkage circle. The traditional SPWM method starts from the perspective of the power supply to generate a sine wave power supply with adjustable frequency and voltage, while the SVPWM method considers the inverter system and the asynchronous motor as a whole, the model is relatively simple, and it is also convenient for the microprocessor to realize real-time control.