Abstract:
A power factor correction converter capable of fast adjusting load functions to (a) convert a single-phase AC voltage into a DC voltage output; (b) control an input current and an input voltage for a correspondent electrical phase, namely the power factor that is 1; and (c) control a DC output voltage level. The converter is provided with a booster-based AC-DC converter as a core, in which the circuit includes a rectification circuit, a switching circuit consisting of a DC inductor and a power crystal, an energy-saving capacitor, a protection circuit, a microprocessor, and auxiliary circuits around. The power factor control, output voltage, and current control and filter modules function in the form of software program instead of conventional hardware circuits. Further, a powerful controller uses an output current feedback to enhance the DC output voltage to suppress the disturbance of load.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a power factor correction converter capable of fast adjusting load. 
     2. Description of the Prior Art 
     With reference to  FIG. 1  shown as a schematic view illustrating a conventional single-phase rectification circuit, a bridge rectification circuit  10  consists of four diodes  11 ,  12 ,  13 , and  14  that are connected in parallel to an output capacitor C 1 . An AC power P 1  is further connected across the bridge rectification circuit  10 . When the AC power P 1  is positive, the input current is transmitted through diodes  11  and  13 ; when the AC power P 1  is negative, the input current is transmitted through diodes  12  and  14  and then filtered by the output capacitor C 1 , a DC power being thereby obtained. Although the structure of rectification circuit is advantageously simplified, the bridge rectification circuit  10  that charges the output capacitor C 1  easily causes a very high surge current impacting other sets of electrical equipment. 
     With cross reference to  FIG. 2  shown as a view of an output voltage waveform generated from the single-phase rectification circuit in  FIG. 1 , when the input voltage waveform W 1  generated from the AC power is a sine wave and the output power waveform W 2  contains DC power, the surge current W 3  generated from the input bridge rectification circuit  10  is not a sine wave; in addition to inferior power factor, the surge current makes the capacity of components and wiring circuit increase, the loss of power supply system thereby directly increasing and other users applying a power distribution system being thereby indirectly affected. 
     Owing to the poor effects derived from the conventional manners, in many prior arts, the technology of power factor amendment is used to improve the art. With different components, the technology of power factor amendment may be divided into passive and active power factor correction. The circuit of passive power factor correction is easily designed, in which a filtering circuit consists of an inductor and a capacitor (not shown) is added between the bridge rectification circuit  10  and an AC power P 1  to moderate the surge current for enhancement of the power factor. However, in such a manner, the total harmonic distortion of input current is high, the physical volume is extremely high, and the power factor is not effectively improved. 
     In the aspect of active power factor correction, the circuit is more complicatedly designed and a switch component must be added in the circuit; further, in the electrical and electronic technology, an adequate control manner is applied to turn ON or OFF the active power switch, and thus the input power current is made to approach the sine wave and follow the input power voltage; the power factor may reach 0.97 or above and there are advantages of low physical volume, low weight, and low total current harmonic distortion. 
     With reference to  FIG. 3  shown as a schematic view illustrating a conventional control circuit provided with a single-phase active PFC specific IC (UCC3854), a potential-divider resistor  20  is mainly used to obtain a DC output voltage feedback signal and, after the signal is compared by a voltage amplifier  21  with a DC voltage command V ref , a voltage differential signal A is obtained; then after the signal is rectified by the diode-based bridge rectifier  22 , an input voltage signal B is obtained by a resistor  23  and multiplied through a multiplexer  24 . Thus, a sine current command co-phase with the input voltage, the amplitude of which is adjusted according to the variation of a load may be obtained. After square times of signal C transmitted through a low-pass filter  25  to the multiplexer  24  is obtained, the signal C is divided by the product of voltage differential signal A and the input voltage signal B; in such a manner, the gain of loop formed by the voltage amplifier  21  may be kept constant and the output is made to serve as a power control. Thus, the variation of input power  26  that is allowed by the system may increase. Next, the sine current command is compared with the feedback of a real input current in a current amplifier  28  and then a current differential compensation signal may be obtained. Further, the current differential compensation signal is compared with a sawtooth wave or a triangle wave V s  in a Pulse Width Modulation (PWM) and then a pulse modulation signal is obtained; next, the signal is converted by a Gate Driver  30  into a drive signal for the active power switch  31  to control the amplitude of duty cycle of the power switch  31 . When the real input current is higher than the sine current command, a negative value or a lower current differential compensation signal is obtained from the current amplifier  28  to reduce the duty cycle; otherwise, the duty cycle increases. Thus, the input current may follow the sine current command to vary for making the phase of current of the input power  26  corresponds to that of voltage of the input power  26  and thus increasing the power factor. However, there are many defects in the conventional correction circuit, such as what is described below.
         (A) Being implemented with hardware, the structural control circuit is easily limited to the characteristics of all circuit components, and errors caused in a manufacturing process, so it is not easy to implement the control strategy.   (B) With reference to  FIG. 4 , because the sine current command is obtained according to the input voltage signal B detected by the resistor  23 , when the voltage of input power  26  forms a non-pure sine wave, if the current command W 4  is applied in this case, harmonic content is contained; thus, the current of real input power  26  and the identical harmonic content of input voltage cause the power factor to be impacted and generate high frequency harmonics of current of the input power  26  that turn worse the quality of power of the power supply system.   (C) Owing to the non-linear characteristic of rectification filtering, the conventional active power factor correction converter causes second harmonics of the power frequency of DC output voltage. In order to reduce the impact of second harmonics, a first-order RC low-pass filter the frequency of which ranges from 10 Hz to 20 Hz is generally added in the path of voltage feedback. Although, in this manner, the second harmonics in the feedback loop may be attenuated to keep stable the DC output voltage, the bandwidth is thus limited, the dynamic response of system being thereby poor. Consequently, when fast DC output voltage connection varies the load, the output voltage cannot be stable. The maximum output voltage overshoot and dip that are caused by the load variation significantly increases to indirectly turn worse the effect of improvement of the power factor and input current harmonics.       

     With cross-reference to US patent No. 2006245219, titled Digital Implementation of Power Factor Correction, a digital circuit is provided to implement a conventional active power factor correction converter, and it is disclosed that the feedback voltage is fed forward to a current loop command input terminal to enhance the dynamic response of output voltage. 
     With cross-reference to Taiwan Laid-Open patent No. 200423516, titled Power Supply Controller for a drive motor of a sports apparatus, a digital processor is used to implement a conventional active power factor correction converter, and it is closed that an input voltage waveform is read in the manner of table lookup to be a basis of modulation of an input current waveform. 
     Consequently, because of the technical defects of described above, the applicant keeps on carving unflaggingly through wholehearted experience and research to develop the present invention, which can effectively improve the defects described above. 
     SUMMARY OF THE INVENTION 
     A power factor correction converter capable of fast adjusting load according to this invention is provided to improve the prior art in manners described below.
         A. The control strategy according to this invention is fully implemented with a microprocessor and its software. In a digital system, a software algorithm and logical judgment is used to implement the control strategy, so the amendment of strategy and the adjustment of parameters are significantly more flexible than those in the aspect of analog control. Further, there are fewer components applied in the digital system and all signals are digitally processed, so the system is not easily interfered and is featured with high reliability.   B. In this invention, an external zero voltage crossover detection circuit is used to detect that a digital pulse signal is generated when the phase of rectification output voltage is 0 degree, and a high frequency signal of digital pulse is generated and inputted through the microprocessor by a built-in counter and a software program; next, the signal is used to look up a sine-wave table built in the microprocessor to generate a sine wave in 0 through 180 degree, serving as a basis upon which the input current waveform is calculated by software. In this invention compared with the prior art, the current command followed by the input power current detects the phase of input power voltage as a basis instead of the waveform. With cross reference to  FIG. 5 , when the voltage of input power  26  is not a pure sine wave, the current command W 5  is still a sine wave, which may effectively solve the current waveform harmonics caused by the input voltage harmonics. Further, the manner of detecting the voltage waveform from the rectification output terminal may also reduce and simplify the length and calculation complexity of a sine wave table built in the microprocessor to increase the system reliability and reduce the cost. The voltage measurement may also simplify the circuit design, in which the microprocessor and the measurement circuit are directly connected for the DC output voltage as a common reference ground potential.   C. In order to solve the defects of dynamic response of prior art, a powerful controller design is provided in this invention to enhance the capability of system controlling the load disturbance in that when the DC output terminal is connected to a fast variation load, such as a motor driver, a required stable DC output voltage may be supplied. In this invention, an adequate transient compensation signal is obtained from the output load current through a properly designed high-pass filter to serve as an extra command added to the current loop for supplying the extra current compensating the load disturbance. When the disturbance ends, the transient compensation signal disappears automatically to make the system control re-function for normal adjustment of voltage loop parameters.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view illustrating a conventional single-phase rectification circuit; 
         FIG. 2  is a view of an I/O voltage waveform generated from the single-phase rectification circuit shown in  FIG. 1 ; 
         FIG. 3  is a schematic view illustrating a conventional control circuit provided with a single-phase active PFC specific IC (UCC3854); 
         FIG. 4  is a view of a waveform generated when the input power voltage is a non-pure sine wave that is shown in  FIG. 3 ; 
         FIG. 5  is a view of a waveform generated when the input power voltage is a non-pure sine wave according to this invention; 
         FIG. 6  is a schematic view illustrating a circuit in a preferred embodiment of this invention; 
         FIG. 7  is a view of a waveform generated by a voltage step-down circuit and a zero voltage crossover detection circuit; 
         FIG. 8  is a schematic view illustrating a calculation flow of a sine signal calculator according to this invention; 
         FIG. 9  is a view of a measured waveform illustrating the overload (400 W) of an AC input voltage 110V according to this invention; 
         FIG. 10  is a view of a measured waveform illustrating the step load variation (rated load ranging from 10% to 100%) when a powerful controller is not added in this invention; 
         FIG. 11  is a view of a measured waveform illustrating the step load variation (rated load ranging from 10% to 100%) when a powerful controller is added in this invention; and 
         FIG. 12  is a view of a measured waveform illustrating the periodic (4 Hz) step load variation (rated load ranging from 10% to 100%) when a powerful controller is added in this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Now, the present invention will be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed. 
     With reference to  FIG. 6  shown as a schematic view illustrating a circuit in a preferred embodiment of this invention, the structure according to this invention is a booster-based AC-DC converter. The circuit comprises at least one input power  41 , one rectifier  42 , one power factor correction component  43 , one power switch  44 , one diode  45 , one energy-saving component  46 , one voltage sensor unit  47 , and a gate driver  48 . In the preferred embodiment of this invention, the rectifier  42  is a diode-based bridge rectifier, the power factor correction component  43  is a capacitor, and the voltage sensor unit  47  comprises two potential-divider resistors  471  and  472  that are connected in series. The components are same as those in the prior art and thus they are not described in detail herein. 
     With cross reference to  FIG. 7  shown as a view of a waveform generated by a voltage step-down circuit and a zero voltage crossover detection circuit, for the requirements of this invention, the circuit further comprises a load  49 , a first current sensor unit  50 , a microprocessor  60 , a second current sensor unit  70 , and zero crossover detection unit  80 . The load  49  is connected in series to the first current sensor unit  50  and further connected in parallel to the opposite terminals of potential-divider resistors  471  and  472 . The opposite terminals of potential-divider resistors  471  and  472  define a DC output voltage Vo. In the preferred embodiment of this invention, the first current sensor unit  50  is a resistor or a Hall sensor component and is used to acquire current when the load  49  varies. Next, the microprocessor  60  is connected to the load  49 , the voltage sensor unit  47 , the gate driver  48 , the second current sensor unit  70 , and the zero crossover detection unit  80 . The second current sensor unit  70  is next connected between the rectifier  42  and the power factor correction component  43 . Further, zero crossover detection unit  80  comprises a voltage step-down circuit  81  and a zero crossover detection circuit  82 . The voltage step-down circuit  81  is connected to the two terminals of rectifier  42  and then to the zero crossover detection circuit  82 . The zero crossover detection circuit  82  is further connected to the microprocessor  60  so that the voltage step-down circuit  81  may be used to lower the voltage outputted by the rectifier  64  for acquiring a step-down voltage V 1 . The step-down voltage V 1  matches with the voltage level of zero crossover detection circuit  82 . The reference ground potential of zero crossover detection circuit  82  is identical to the potential of microprocessor  60 . The zero crossover detection circuit  82  converts the voltage lowered by the voltage step-down circuit  81  into a pulse digital signal S 1 . 
     The microprocessor  60  further comprises a powerful controller  61 , a voltage controller  62 , a sine signal calculator  63 , a current controller  64 , and a pulse width modulator  65 . 
     One terminal of the powerful controller  61  is connected through a first analog/digital conversion contact  611  between the load  49  and the first current sensor unit  50  so that the signal from the load  49  may be converted into a load current i s  and then inputted to the powerful controller  61 . The powerful controller  61  further comprises a properly designed high-pass filter  612  and a time delay module  613 . One terminal of the high-pass filter  612  is connected to the first analog/digital conversion contact  611  to acquire the variation of load current i s ; the other terminal is connected to the time delay module  613 , and thus a transient compensation signal i r  is generated by the time delay module  613  to effectively increase the dynamic response of system and further enhance the DC output voltage Vo to suppress the disturbance of load  49 . Besides, through a second analog/digital conversion contact  614 , it is connected between the potential-divider resistors  471  and  472 , a voltage measured from the potential-divider resistor  472  is sent to the second analog/digital conversion contact  614  and then converted into a DC feedback voltage v fb , and the DC feedback voltage v fb  is subtracted by a DC voltage command v* to obtain a voltage error volume v e . The voltage error volume v e  is further sent to the voltage controller  62  and calculated to obtain a current error compensation signal i ref1 , and the current error compensation signal i ref1  is added to the transient compensation signal i r  to obtain a current reference command i ref . Next, a digital input contact  631  is connected between the zero crossover detection circuit  82  and the sine signal calculator  63  to obtain the pulse digital signal S 1  converted by the zero crossover detection circuit  82 . The pulse digital signal S 1  is further inputted to the sine signal calculator  63 . 
     With reference to  FIG. 8  shown as a schematic view illustrating a calculation flow of a sine signal calculator according to this invention, the sine signal calculator  63  converts the pulse digital signal S 1  through a timer  632  into an increment address data. The data is further added to a starting address  633  in a sine wave table to obtain a memory address of sine wave to be measured, and the memory address is used through a sine wave table  634  to acquire an input current waveform (sin θ)W 6 . The rising edge of pulse digital signal S 1  resets the address data of timer  632  to zero to make the output of input current waveform W 6  show a periodic output the frequency of which is same as that of pulse digital signal S 1 . Besides, in the sine wave table  634 , the contents of input current waveform ranging from 0 degree to 180 degree are stored from a lower address of memory. Next, the input current waveform W 6  is multiplied by the current reference command i ref  to obtain a sine current command i*, and the amplitude of sine current command i* may be changed and adjusted according to the load  49 . Further, the microprocessor  60  is connected through a third analog/digital conversion contact  635  to the second current sensor unit  70  to acquire a real input current i fb . The real input current l fb  is subtracted by the sine current command i* to obtain a current error volume i e . For the current error volume i e , a current error compensation signal i ref1  is acquired from the current controller  64 , and then a pulse modulation signal is generated by the pulse width modulator  65  and converted into a drive signal from a digital contact  651  through the gate driver  48  to control the duty cycle of power switch  44 . When the real input current i fb  is higher than the sine current command i*, a negative value or a lower current differential compensation signal is obtained from the current controller  64  to lower the duty cycle; otherwise, the duty cycle increases. Thus, the real input current i fb  stands for a minimum error volume may follow the sine current command i* to vary for achievement of the cophase voltage and current of input power  41  and thus increase of the power factor. In addition to the stable DC output voltage V 0  that may be acquired, the phase of current of the input power  41  is made to further approach the voltage of input power  41  for achievement of the requirements of power factor that is 1. 
     With reference to  FIG. 9  shown as a view of a measured waveform illustrating the full load (400 W) of an AC input voltage 110V according to this invention, when the AC voltage of input power  41  is 110V/60 Hz, the DC output voltage is Vo 200V, and the load  49  is full (400 W), the power factor may reach 0.997 that is obtained from the input voltage waveform  126  and input current waveform  128  measured from the input power  41 . 
     with reference to  FIGS. 10 and 11  respectively shown as a view of a measured waveform illustrating the step load variation (rated load ranging from 10% to 100%) when a powerful controller is not added in this invention, and a view of a measured waveform illustrating the step load variation (rated load ranging from 10% to 100%) when a powerful controller is added in this invention, it is apparent that when the powerful controller  61  is applied for a compensation strategy, the amplitude depth, overshoot, and setting time that are generated from the output voltage waveform  130  of DC output voltage V 0  may be well improved, and the input current waveform  128  is then improved. 
     With cross reference to  FIG. 12  shown as a view of a measured waveform illustrating the periodic (4 Hz) step load variation (rated load ranging from 10% to 100%) when a powerful controller is added in this invention, it is apparent that the output voltage waveform  130  on a DC chain may be stable again; comparatively, from the AC power factor correction converter not provided with the powerful controller  61 , in the same testing condition, the DC output voltage Vo is out of control and thereby a DC-chain output current waveform  132  is generated. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.