Abstract: Has established the voltage PWM rectifier model, proposed that one kind of practical electric current decoupling plan, gives one kind the three-phase voltage PWM rectifier control system which controls by the dsPIC30F4012 microprocessor, introduced in detail its system composition, the control principle and the hardware architecture, elaborate its software flow, gives the experimental result.
Key word: PWMi dsPIC30F4012; Electric current decoupling control; Voltage rectifier
Introduction
In recent years, because in the AC/DC transformation, the PWM rectifier its can realize the high power factor movement, and does not produce the overtone nearly but time is paid attention. Has also carried on about the PWM rectifier’s research in our country many years, its implementation plan mainly has the voltage PWM rectifier and the current mode PWM rectifier. Because the current mode PWM rectifier has the direct-current stored energy inductance and exchanges the LC filter link. Therefore the structure and the control are relatively complex, the system loses in a big way. But the voltage PWM rectifier by it low loss, the simple structure and the control and so on a series of merits becomes the PWM rectifier’s research key.
1 PWM rectifier principle of work
Figure 1 shows the three-phase voltage PWM rectifier main circuit. After the rectifier enters the stable state active status, the output DC voltage is constant, rectification bridge’s three-phase bridge arm according to sine pulse-duration modulation rule actuation. When the turn-on frequency is very high, as a result of inductor’s filter action, the harmonic current which the higher harmonic voltage produces is small, if only considered that the electric current and the voltage fundamental wave, the rectification bridge may regard as is an ideal three-phase AC potential source. The suitable regulating control quantity’s size and the phase, can control the input current the phase, may achieve the change power factor the goal, to controls the input current the size to control spreads to converter’s energy, also has controlled the direct-current side voltage. Obviously the PWM rectifier’s control objective is the input current and the output voltage, but loses the person electric current the control is the key which the rectifier controls. Input current’s control objective is causes the current waveform to become the sine wave, and input voltage with phase.
2 in d-q in coordinate mathematical model [1,2,3]
In the PWM rectifier control method, the author transforms three-phase AC electric current revolving carries on the d-q coordinate system, by to electric current d, the q component carries on the independent control. The active power and reactive power’s adjustment is very convenient.
Figure 1 PWM rectifier U∞, U∞, U∞ respectively be rectification bridge three-phase control voltage, in the right way program:
Uses the space coordinates transform method, transforms the above equation to the two phase static coordinate, its transformation matrix is
Further by α-β the coordinate system transformation is again the d-q two phase revolving coordinate system, the transformation matrix for the transformation equation is
After the above transformation, under the synchronized revolving coordinate system the PWM rectifier equation is:
usd, usq, id, qi. , Ud, Uq respectively are under the d-q synchronization revolving coordinate system’s supply voltage, the input current and the bridge center point control voltage. Take loses the person voltage resultant vectorr the position as the d axis direction, takes three-phase input voltage usc, usb, us is
Undergoes the similar coordinate transformation, has under the d-q synchronization coordinate system
Under the substitution synchronization revolving coordinate system PWM rectifier’s equation (6) type may result in (8) type
Is obvious by this type, between id and iq has the coupling, usually has the voltage forward feed decoupling control and the current feedback decoupling controls two kinds, although the former is one kind of complete linearized decoupling control plan. But timeliness is not good. The author uses the current feedback decoupling control mode, the implementation is convenient, the control circuit is simple.
In practical application. When the electricity pressure ring’s sampling frequency is higher than the network voltage far the frequency, creates the cross coupling in the equation ωLid and ωLid to current regulator performance influence small [1], may neglect, like this current control instruction id*, iq* and feedback electric current id, iq compares, its error after P, the adjustment obtains the voltage demand signal, obtains the approximate decoupling model, namely:
PWM rectifier basic control diagram as shown in Figure 2. When PWM must obtain the specific power factor, then the input current must track the input voltage, in the d-q coordinate system, the input voltage vector will locate on the d axis, such controlling current vector also similarly only then d axis component, but the q axis component is zero. Satisfies iq*=O then. The author uses the double closed-loop control plan which the voltage outer ring and the electric current inner rim unify. id* is the voltage regulator outputs, it is proportional with the wattful current.
3 hardware circuit composition
This system uses Microchip Corporation to help the digitized PWM rectifier specially for the electrical machinery high-speed control production dsPIC30F4012 16 microprocessors as the core control circuit group. dsPI (230F4012 has 1 16 CPU and 1 dSP essence, when the interior highest clock rate is 120MHz, carries on a 16bitxl6bit operation the time is 8.3ns: Moreover includes 2048 byte register RAM, the 48KB internal procedure space, 1024 bytes, EEPR()M, interrupts 7 I/0 the mouth altogether 21 I/0 mouth line, some 1 group full-duplex’s UART functional module, 1 synchronized serial SPI functional module, 1 FC serial communication module and 1 CAN serial communication module, internal are equipped with 1 6 channel’s A/D switch, works in 10 patterns, the sampling maintains the time, the switching time, the threshold detection way and the zero-bias compensation adjusts programmable; 5 16 timers; Some 4 groups catchers, 2 group comparison/standard pulse-duration modulation unit (PWM) module; 1 6 channel’s electrical machinery special-purpose MCPWM controller. in dsPIC30F4012 M (2PWM the electrical machinery special-purpose PWM controller is one of its design characteristics; This establishment simplified greatly has produced the PWM profile control software and the external hardware. May produce through the programming independent, has the same frequency and the working three-phase 6 group PWM profile. And signals gives the rectifier by RE the mouth direct output 6 group PWM. Each pin drive current reaches 25mA, to prevent on the identical bridge arm 2 power tubes to go nonstop to creates the short circuit. This generator may also through the programming establishment dead area interlock time, when external clock 10MHz after the internal 8 frequency multiplication system clock be 80MHz, the dead time scope divides into the coefficient according to the frequency division coefficient is time differently 1:1 for 50ns~3.15μs; The coefficient is when l:2 is 100ns~6.3μs, the coefficient is when 1:4 is 200ns~12.6μs: The coefficient is when 1:8 is 400ns~25.2μs.
Figure 3 shows the system composition diagram, this plan’s hardware mainly by the input voltage phase and the peak-to-peak value examination, the input current examination, the output voltage examination, the actuation and the protection circuit and so on is composed. The electric current and the voltage examination use the Hall sensor, after undergoing the suitable signal conversion, inputs to the dsPIC30F4012 A/D end. The driving circuit uses EXB841.
4 system softwares design [4]
The system software is mainly composed of the master routine and two interrupt servicing subroutine. The master routine part is mainly carries on the initialization to the control software, establishes dsPIC30F4012 each kind of functional module, establishes the system each functional module the working. The system contains two interrupt service, namely outage service routine and capture mouth interrupt service. The capture mouth interrupt servicing subroutine class’s function is carries on the localization to the input signal. The outage service routine uses for to complete the voltage, the electric current adjustment and outputs the PWM signal to the hardware circuit, controls the switching valve, thus achieves controls main circuit’s goal. Simultaneously completes each kind of software protection the inquiry and the output guard signal function, Figure 4 shows the outage service subroutine the flow.
5 experimental results and conclusion
Based on the dsPIC30F14012 voltage PWM rectifier’s input exchange phase voltage is 220V, the output DC voltage is 600V. The input inductance is 7.5mH, the rectification load for 50Ω. This system main circuit uses Mitsubishi Corporation’s CMl50DY-24H 150A/1200V IG-BT, the actuation uses the EXB84l thick-film circuit. The experiment proved: Electric current basically for sine wave, and is the same with the voltage waveform, has realized the specific power factor, obtains electric current total distortion factor (THP) with the electric power harmonic analyzer is 3.8%.
Through to the PWM rectifier’s under d-q coordinate mathematical model’s inferential reasoning and the analysis, proposed under one suitable d-q coordinate system’s approximate decoupling control method. And uses the function formidable dsPIC30F4012 microprocessor to realize the entire digitized PWM rectifier as the core. From the experimental result looked that the effect is good. Has the good application prospect
