Abstract:
The present invention relates a waveform transformation method and apparatus. It uses multilevel transformation module in series, and the output voltages of power modules at all levels are superposed to get the total output voltage, whereas each power transformation module realizes AC-to-AC direct conversion. The deviation between the output′ voltage and setting reference voltage at any time point is made as small as possible by selecting different transformation modules as current working circuit and selecting output voltage waveform of the each different transformation modules. The invention includes outputting n groups of electrical insulating AC and n transfonnation modules connected with AC. The wave transformation method and device of present invention eliminates the intermediate DC stage, so that the circuit is greatly simplified, the cost is reduced obviously and improve working efficiency. It makes voltage and current harmonics to be reduced and obtains higher power factor.

Description:
FIELD OF INVENTION 
     The present invention is related to a wave transformation method and device in high voltage switch field. More particularly, this invention is related to a variable-frequency drive or variable-frequency power supply for motors. 
     BACKGROUND OF INVENTION 
     Frequency converters and variable-frequency power supplies are widely used as driving units for AC (alternating current) motors and so on, and most of them employ AC-AC conversion or AC-DC (direct current) conversion mode. The existing technology for AC-AC frequency converters utilizes direct AC-AC conversion and output Volt Alternating Current (VAC) through altering the triggering angle of a switch component. Such a solution achieves a relative low power factor and may result in heavy harmonic wave pollution to the electric network and electric devices. On the other hand, the existing technology for voltage-type AC-DC-AC general-purpose frequency converters employs pulse-width modulation (PWM) method (i.e., perform switching control of intermediate DC voltage with a semiconductor switch component) to output VAC. Such a solution increases equipment cost and decreases working efficiency of equipment due to existence of the intermediate DC stage. Above problems are more severe in high capacity frequency converters and variable-frequency power supplies. 
     DESCRIPTION OF INVENTION 
     The object of the present invention is to provide a wave transformation method and device which eliminate the intermediate DC stage in order to reduce the cost of the device and improve working efficiency, and it is still a further object of the preset invention to provide a wave transformation method and device to delivers smaller voltage harmonics and higher power factor. 
     The AC-AC wave transformation device in the present invention comprises n transformation modules. The input terminals of those transformation modules are connected to n groups of electrical insulating AC. Each group has m phases. The output ends of those transformation modules are connected in series to form a total voltage output. Each of those transformation modules further comprises power semiconductor switch components or power semiconductor switch component groups to form a bi-directionally controllable m-phases rectification circuit, the output polarity of which is variable. 
     The transformation module in the device is a full-wave bi-directionally controlled m-phases rectifying circuit whose output polarity is variable. The full-wave bi-directionally controlled m-phases rectifying circuit consists of power semiconductor switching components or power semiconductor switching component groups connected. The full-wave bi-directionally controlled m-phases rectifying circuit consists of 2×m power semiconductor switching components or power semiconductor switching component groups. Each of power semiconductor switching components or power semiconductor switching component groups is connected respectively between m input lines and two output lines. 
     The transformation module in the device can also be a half-wave bi-directionally controlled m-phases rectifying circuit whose output polarity is variable. The half-wave bi-directionally controlled m-phases rectifying circuit consists of power semiconductor switching components or power semiconductor switching component groups connected. The half-wave bi-directionally controlled m-phases rectifying circuit consists of m+1 power semiconductor switching components or power semiconductor switching component groups, wherein m power semiconductor switching components or power semiconductor switching component groups are connected respectively between m input lines and output lines; and one power semiconductor switching component or power semiconductor switching component group is connected respectively between the input neutral line and output line. 
     The transformation module in the device is a bi-directionally semi-controlled m-phases rectifying circuit whose output polarity is variable. The bi-directionally semi-controlled m-phases rectifying circuit consists of power semiconductor switching components or power semiconductor switching component groups connected. The bi-directionally semi-controlled m-phases rectifying circuit consists of 2×m power semiconductor switching components or power semiconductor switching component groups, each of which is connected respectively between m input lines and two output lines. 
     The power semiconductor switching components in the device are bi-directional thyristors. 
     The power semiconductor switching component groups in the device are either unidirectional thyristors which are positive-negative connected in parallel, or IGBTs which positive-negative are connected in series, or turn-off thyristors which are positive-negative connected in parallel, or IGCTs which are positive-negative connected in parallel, or turn-off thyristors which are positive-negative connected in series, or IGCTs which are positive-negative connected in series. 
     The AC-AC waveform transformation method of the present invention includes the following steps: 
     1} setting a sine-wave voltage to be output, and dividing the sine-wave according to time interval t 0 , t 1 , t 2 , t 3  . . . ti, and selecting the voltage waveform during t 0 ˜t 1  as the given reference voltage; 
     2} selecting j groups from the n groups of m phases AC power supply that are electrically insulated to each other as the present input voltage, where j≦n; 
     3} performing bi-directionally controllable rectification on the rest (n-j) groups m phases AC, so that its output voltage is 0, 
     4} for the selected j groups of m phases AC which are electrically insulated each other, selecting one voltage waveform for each group from all voltage waveforms output during t 0 ˜t 1  after carrying out bi-directionally controllable rectification on j groups of m phases AC voltage so that j voltage waveforms are obtained by performing bi-directionally controllable rectification on j groups of electrical insulating m phases AC; 
     5} finding the sum of above-mentioned j voltage waveforms to get a total calculated output voltage; 
     6} comparing the calculated output voltage during t 0 ˜t 1  with the above-mentioned given reference voltage; selecting m phases AC power supplies of different groups from the above-mentioned n groups of m phases AC that are electrically insulated to each other as current input voltages; among the m-phase AC power supply of each group, selecting different voltage waveforms that have gone through bi-directionally controllable rectification, so that the difference between the calculated output voltage and given reference voltage is made as low as possible at any time, and the total harmonics in the output voltage is made the smallest or some high-order harmonics is made as low as possible, or the total harmonics in the sum of current for n groups of AC power supplies is made the smallest or some high-order harmonics is made as low as possible; or the average leading or lagging power factors of each in the n inputting groups is made as large as possible; 
     7} determine the working status of each bi-directionally controllable rectifying circuit based on the voltage waveform corresponding to each selected m-phase AC power supply, and performing bi-directionally controllable rectification in accordance to the working status determined in above way; 
     8} selecting the given expected voltage waveforms during t 1 ˜t 2 , t 2 ˜t 3 , ti−1˜ti as given reference voltages respectively and repeat step 2˜8, and obtain the desired AC output voltages. 
     In above mentioned method, the n groups of m phases AC power supply that are electrically insulated to each other and is obtained by way of insulated transformation or insulated phase-shift transformation of a total AC power supply. 
     The wave transformation method and device of present invention eliminates the intermediate DC stage, so the circuit is greatly simplified, therefore it can reduce the cost and improve working efficiency, deliver smaller voltage and current harmonics and higher power factor. 
    
    
     
       DESCRIPTION OF FIGURES 
         FIG. 1  is the circuit diagram of the device of present invention. 
         FIG. 2  is the full-wave bi-directionally controlled rectifying circuit included in the transformation module of the device of present invention. 
         FIG. 3  is the half-wave bi-directionally controlled rectifying circuit included in the transformation module of the device of present invention. 
         FIG. 4  is the bi-directionally semi-controlled rectifying circuit included in the transformation module of the device of present invention. 
         FIG. 5  is the bi-directionally controlled rectifying circuit consisting of bi-directional thyristors. 
         FIG. 6  is the bi-directionally controlled rectifying circuit consisting of thyristors. 
         FIG. 7  is the bi-directionally semi-controlled rectifying circuit consisting of turn-off IGBTs. 
         FIG. 8  is the full-wave bi-directionally controlled rectifying circuit consisting of turn-off IGBTs. 
         FIG. 9  is the full-wave bi-directionally controlled rectifying circuit consisting of turn-off thyristors or IGCTs in series. 
         FIG. 10  is the full-wave bi-directionally controlled rectifying circuit consists of turn-off thyristors or IGCTs in parallel. 
         FIG. 11  is the sine-wave voltage to be output. 
         FIG. 12  is an output voltage waveform selected for bi-directionally controlled rectifying circuit. 
         FIG. 13  is the second output voltage waveform selected. 
         FIG. 14  is the third output voltage waveform selected. 
         FIG. 15  is the fourth output voltage waveform selected. 
         FIG. 16  is the overlapped output voltage waveform 
         FIG. 17  is an example of the device of present invention, wherein,  1  indicates first-grade transformation module;  2  indicates second-grade transformation module;  3  indicates third-grade transformation module;  4  indicates fourth-grade transformation module;  5  indicates fifth-grade transformation module;  10 - 19  indicates thyristors forming the bi-directionally controlled rectifying circuit 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The principle of the present invention and the working process of the device will be described in detail below in connection with attached figures. 
       FIG. 1  is the circuit diagram of the device designed by present invention. Referring to  FIG. 1 , the input terminals of transformation module  1 , transformation module  2  . . . transformation module N are connected respectively with input AC power supplies V 11 , V 21 , . . . VM 1 ; V 12 , V 22 , . . . VM 2 ; V 1 N, V 2 N, . . . VMN, and the output terminals of transformation module  1 ,  2  . . . M are connected in series so that a total output voltage VO is produced. 
       FIG. 2  is the full-wave bi-directionally controlled rectifying circuit included in the transformation module of the device of present invention. Referring to  FIG. 2 , the switching component K 1 , K 2 , . . . Km, Km+1, Km+2, . . . K 2   m  are connected to form a full-wave bi-directionally controlled m phases rectifying circuit. Each power semiconductor switching component or power semiconductor switching component group is connected respectively between m input lines and two output lines, their input terminals are connected to m-phase AC voltage V 1 , V 2  . . . Vm, the output voltage is VO. 
       FIG. 3  is the half-wave bi-directionally controlled rectifying circuit included in the transformation module of the device of present invention. Referring to  FIG. 3 , the switching component K 1 , K 2 , . . . Km, Km+1 are connected together to form a half-wave bi-directionally controlled m phases rectifying circuit, their input terminals are connected to m-phase AC voltages V 1 , V 2 , . . . Vm and neutral line N, where, m power semiconductor switching components or power semiconductor switching component groups are connected respectively between m input lines and output lines, one power semiconductor switching component or power semiconductor switching component group is connected between the inputting neutral line and output line, the output voltage is VO. 
       FIG. 4  is another circuit structure in the transformation module of the device of present invention. Referring to  FIG. 4 , each switching component includes a diode and a switch, the switching component K 1 , K 2 , . . . Km, Km+1, Km+2, . . . K 2   m  are connected together to form a bi-directionally semi-controlled m phases rectifying circuit, each power semiconductor switching component or power semiconductor switching component group is connected respectively between m input lines and two output lines, their input terminals are connected to m-phase AC voltage V 1 , V 2 , . . . Vm, the output voltage is VO. 
       FIG. 5  is the circuit diagram of the transformation module consists of bi-directional thyristors. Referring to  FIG. 5 , bi-directional thyristor K 1 , K 2 , . . . Km, Km+1, Km+2, . . . K 2   m  are connected together to form a bi-directionally controlled m phases rectifier-bridge circuit, each power semiconductor switching component is connected respectively between m input lines and two output lines, their input terminals are connected to m-phase AC voltage V 1 , V 2 , . . . Vm, the output voltage is VO. 
       FIG. 6  is the circuit diagram of the transformation module consists of unidirectional thyristors. Referring to  FIG. 6 , each switching component includes two thyristors connected reversely in parallel, the switching component K 1 , K 2 , . . . Km, Km+1, Km+2, . . . K 2   m  are connected together to form a bi-directionally controlled m phases rectifying circuit, each power semiconductor switching component group is connected respectively between m input lines and two output lines, their input terminals are connected to m-phases AC voltage V 1 , V 2 , . . . Vm, the output voltage is VO. 
       FIG. 7  is the circuit diagram of transformation module consists of IGBTs. Referring to  FIG. 7 , each switching component group includes one IGBT and two diodes, and after the IGBT is connected to a diode in series, it is connected in series to another diode. The switching component formed in this way K 1 , K 2 , . . . Km, Km+1, Km+2, . . . K 2   m  are connected to form a bi-directionally semi-controlled m phases rectifying circuit, each power semiconductor switching component group is connected respectively between m input lines and two output lines, their input terminals are connected to m-phases AC voltage V 1 , V 2 , . . . Vm, the output voltage is VO. 
       FIG. 8  is the circuit diagram of transformation module consists of IGBTs. Referring to  FIG. 8 , each switching component group includes two IGBTs which are connected reversely in series each other, the switching component formed in this way K 1 , K 2 , . . . Km, Km+1, Km+2, . . . K 2   m  are connected to form a bi-directionally controlled m phases rectifying circuit, each power semiconductor switching component group is connected respectively between m input lines and two output lines, their input terminals are connected to m-phases AC voltage V 1 , V 2 , . . . Vm, the output voltage is VO. 
       FIG. 9  is the full-wave bi-directionally controlled rectifying circuit consists of turn-off thyristors or IGCTs in series. Referring to  FIG. 9  each switching component includes two bi-directional thyristors or IGCTs which are connected reversely in series each other, the switching component formed in this way K 1 , K 2 , . . . Km, Km+1, Km+2, . . . K2m are connected to form a bi-directionally controlled m-phases rectifying circuit, each power semiconductor switching component group is connected respectively between m input lines and two output lines, their input terminals are connected to m-phases AC voltage V 1 , V 2 , . . . Vm, the output voltage is VO. 
       FIG. 10  is the full-wave bi-directionally controlled rectifying circuit consists of turn-off thyristors or IGCTs in parallel. Referring to  FIG. 10 , each switching component group includes two bi-directional thyristors or IGCTs which are connected reversely in parallel each other, the switching component formed in this way K 1 , K 2 , . . . Km, Km+1, Km+2, . . . K 2   m  are connected to form a bi-directionally controlled m-phases rectifying circuit, each power semiconductor switching component group is connected respectively between m input lines and two output lines, their input terminals are connected to m-phases AC voltage V 1 , V 2 , . . . Vm, the output voltage is VO. 
     The power semiconductor switching component group in the device of present invention can also consist of one or more field effect transistors, IGCTs, IGBTs, MCTs, SITs; or consist of one or more field effect transistors, IGCTs, IGBTs, MCTs, SITs and one or more diodes. 
     The process of waveform transformation designed in present invention will be described in detail below. To make it clear, we take the embodiment circuit in  FIG. 17  as example. 
       FIG. 11  is the waveform of expected value for given output sine-wave voltage, and it is divided into parts according to time t 0 , t 1 , t 2 , t 3 , First, the given expected voltage waveform during t 0 ˜t 1  of  FIG. 8  is selected as the given reference voltage. 
     The bi-directionally controlled rectifying circuit of transformation module  1 ,  2 ,  3  and  4  in  FIG. 17  is selected as current working circuit, and turn on thyristor  16 ,  17 ,  18  and  19  in the bi-directionally controlled rectifying circuit of transformation module  5 , so that bi-directionally controlled rectifying circuit  5  is under no-working state. 
     Next, the output voltage waveform for bi-directionally controlled rectifying circuit of each transformation module is selected as current working circuit: 
     For the bi-directionally controlled rectifying circuit of transformation module  1  in  FIG. 17 , the three-phase input voltages of the circuit respectively are assume as following:
 
 va=uk  sin(ω t );
 
 vb=uk  sin(ω t− 2/3π);
 
 vc=uk  sin(ω t− 4/3π);
 
wherein, uk is a constant.
 
     For the different ON-OFF states of thyristors in the circuit, it may corresponds to various output voltage, e.g. when thyristor  10 ,  14  are turned on at ωt=t 0 , its output voltage waveform at t 0 ˜t 1  is (va-vb); when thyristor  11 ,  15  are turn on at ωt=t 0 , its output voltage waveform at t 0 ˜t 1  is (vb-vc); when thyristor  12 ,  13  are turn on at ωt=t 0 , and thyristor  14  is turned on at ωt=⅚π, its output voltage waveform is (vc-va) (when ωt=t 0 ˜⅚π) and (vc-vb) (when ωt=⅚π˜t 1 ). The output voltage waveform selected for transformation module  1  in this example is (va-vb) (when ωt=t 0 ˜⅔π) and (va-vc) (when ωt=⅔π˜t 1 ) as shown in  FIG. 12 , and the corresponding ON-OFF state of thyristors are: thyristor  10 ,  14  are turned on at ωt=t 0 , and  15  is turned on at ωt=⅔π. With this method, the output voltage waveform for transformation module  2  as shown in  FIG. 13 , that for module  3  as shown in  FIG. 14 , and that for module  4  as shown in  FIG. 15  are selected. 
     The above selected output voltage waveforms for transformation module  1 ,  2 ,  3  and  4  are superposed to obtain the voltage waveform shown in FIG.  16 . The waveform during time t 0 ˜t 1  is compared with the given reference voltage during time t 0 ˜t 1  (as shown in FIG.  11 ), the differences at different points are low, and according to Fourier transformation frequency analysis, the harmonic voltage in the output is at minimum, so it is taken as a group of an optimal output voltage waveform finally selected. If the output harmonic voltage is not minimal, it is necessary to re-select the transformation module as current working circuit or re-select the output voltage waveform of each transformation module. 
     Based on the optimal output voltage waveform for bi-directionally controlled rectifying circuit of each transformation module selected according to above-mentioned way, ON-OFF state of each thyristor during t 0 ˜t 1  is determined, and trigger signal is sent to each thyristor, hence the desired output voltage Vo is obtained.