Patent Publication Number: US-2023134084-A1

Title: High-frequency power supply device and output control method therefor

Description:
TECHNICAL FIELD 
     The present invention relates to a high-frequency power supply device to be applied to a plasma generation device and others, in particular a high-frequency power supply device comprising an AC-DC converter for converting an input from a three-phase AC source into a direct current and a high-frequency amplifier including a plurality of FET elements, and to an output control method therefor. 
     BACKGROUND ART 
     A high-frequency power supply device is applied as a power supply device for ultrasonic oscillation, induced electromotive force generation, plasma generation or others, and there is a known power supply device as one example that converts an input from a three-phase AC source into a direct current (DC), and then converts it into high-frequency AC power by means of a DC-RF conversion unit to thereby output the AC power. As such a high-frequency power supply device to be applied to a plasma processing system, for instance, Patent Literature 1 discloses a high-frequency power source comprising any amplifier of high frequency or the like, which includes an AC-DC conversion unit, a DC-DC conversion unit, a high-frequency generation unit (AC power output means), an RF detection unit and an RF power control unit, in which a DC-RF conversion unit includes MOSFETs as switch elements, so as to convert an input from an AC commercial power source into certain high frequency AC power. With such a high-frequency power source, it is said that output power can be stably and suitably controlled in a wide range. 
     Citation List 
     Patent Literature 
     [Patent Literature 1] Japanese Patent Laid-Open Publication No. 2015-144505 
     SUMMARY OF THE INVENTION 
     Problems to Be Solved by the Invention 
     In the conventional high-frequency power source described above, when an input from a three-phase commercial power source is converted into a direct current by the AC-DC conversion unit, an output thus obtained is accompanied by voltage fluctuations, which are so-called “ripples”. Thus, the output is processed by the DC-DC conversion unit to reconvert into a DC voltage with the ripples being removed, and sent to the DC-RF conversion unit. At this time, in the case of performing the output control by the DC-RF conversion unit, a response speed in the high-frequency amplifier that constitutes the DC-RF conversion unit is dependent on a response speed, which is an input, in the DC-DC conversion unit. 
     A typical DC-DC conversion unit (converter) consists of an inverter and a rectification circuit or chopper circuit, each component including a switching element as well as an LC filter for smoothing an output. In order to reduce the above-mentioned ripples by the DC-DC conversion unit, a resonance frequency in the LC filter is usually set to be equal to or less than one-tenth of a switching frequency of each switching element. 
     Furthermore, as disclosed in the high-frequency power source of Patent Literature 1, when an output from the RF detection unit is detected to perform feedback control on the DC-DC conversion unit, it is necessary to set a response frequency in a feedback loop to be much lower than the resonance frequency in the LC filter that corresponds to an output from the DC-RF conversion unit (e.g., equal to or less than one-tenth of the resonance frequency in the LC filter). Thus, in the high-frequency power source that performs the control of removing the ripples by the conventional DC-DC conversion unit, since a response speed of an output voltage depends on the switching frequency in the DC-DC conversion unit and is about one hundredth of the switching frequency, there is a problem that it is difficult to perform the output control with a high response frequency of several kHz, several tens kHz or so even by using MOSFETs or similar, which are operable at high speed, to the switching elements of the DC-DC conversion unit. 
     The present invention is for solving the above-described conventional problem, and aims to provide a high-frequency power supply device and an output control method therefor in order to reduce the ripples caused by the DC conversion of the input from the three-phase AC power source and enable the output control at a high frequency band. 
     Means for Solving the Problem 
     In order to solve the above problem, the present invention has a principal aspect that is a high-frequency power supply device including an AC-DC conversion unit that converts an input from a three-phase power source into a direct current, and a high-frequency amplifier that includes a plurality of FET elements and outputs high-frequency AC power, wherein an output from the AC-DC conversion unit is directly input to the high-frequency amplifier. The high-frequency power supply device further includes a phase conversion circuit that provides to a gate signal to be input to each of the plurality of FET elements with a phase difference for cancelling a fluctuation component contained in the direct current. 
      Another aspect of the invention is an output control method for outputting an input from a three-phase AC power source as high-frequency AC power by using a high-frequency amplifier which includes a plurality of FET elements. This method is for converting the input from the three-phase AC power source into a direct current and directly inputting it to the high-frequency amplifier, and providing to a gate signal to be input to each of the plurality of FET elements with a phase difference for cancelling a fluctuation component contained in the direct current to perform switching, so as to generate the high-frequency AC power. 
     In accordance with the invention with the above-described configuration, the input from the three-phase AC power source is converted into the direct current and directly inputted to the high-frequency amplifier, and the phase difference for cancelling the fluctuation component contained in the direct current is provided to the gate signal to be input to each of the plurality of FET elements and thus the switching is performed to generate the high-frequency AC power, thereby enabling to reduce the ripples caused by the direct conversion of the input from the three-phase AC power source while performing the output control at the high frequency band. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram showing schematically a high-frequency power supply device according to a representative example of the invention; 
         FIG.  2    is a circuit diagram showing an equivalent connection circuit of the high-frequency amplifier shown in  FIG.  1   ; 
         FIG.  3    is a time chart showing examples of gate signals input to FET elements shown in  FIG.  2   ; 
         FIG.  4    is a waveform chart showing a relationship between an input (DC voltage) and an output (AC voltage) in the high-frequency power supply device shown in  FIG.  1   ; 
         FIG.  5    is a block diagram showing schematically a high-frequency power supply device according to a variation of the invention; and 
         FIG.  6    is a block diagram showing schematically a high-frequency power supply device according to another variation of the invention. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     A description will now be made about representative illustrative embodiments of a high-frequency power supply device and an output control method therefor according to the present invention by referring to  FIGS.  1  to  6   . 
       FIG.  1    is a block diagram that schematically shows a high-frequency power supply device according to a representative example of the invention. As shown in  FIG.   1   , a high-frequency power supply device  100  includes an AC-DC conversion unit  110  that converts an input from a three-phase power source  10  into a direct current, a high-frequency amplifier  120  that includes a plurality of FET elements  122 A to  122 B′, which will be described later, and outputs a high-frequency AC output V RF , and a phase conversion circuit  130  that provides to a gate signal V gs  to be input to each of the FET elements  122 A to  122 B′ with a phase difference for cancelling a fluctuation component contained in the direct current. The significant feature of the high-frequency power supply device  100  is that an output V DC  of the AC-DC conversion unit  110  is directly input into a high-frequency amplifier  120 . 
     The AC-DC conversion unit  110  is configured as a circuit block that converts an input from a three-phase AC power source  10  for commercial use into a DC voltage V DC , and such circuit block may be a three-phase rectification circuit, a three-phase power factor correction circuit or similar. The high-frequency amplifier  120  is a circuit block that converts the DC voltage V DC  from the AC-DC conversion unit  110  into AC power at a predetermined frequency (high frequency of several hundreds kHz to several tens MHz), whose specific configuration will be described later. 
     The phase conversion circuit  130  includes, as an example, an output detection unit  132  that detects an output voltage or output power output of a high-frequency AC output V RF  from the high-frequency amplifier  120  as an output detection value, an error calculation control unit  134  that determines an amount of operation for controlling a phase difference in the gate signal V gs  to be input to the high-frequency amplifier  120  based on a difference between the output detection value detected in the output detection unit  132  and an output command value, and a gate signal generation circuit  136  that generates the gate signal V gs  to be input to each of the FET elements  122 A to  122 B′ of the high-frequency amplifier  120  when the phase difference is adjusted according to the amount of operation determined by the error calculation control unit  134 . The error calculation control unit  134  is grounded through an output command  138 , and calculates an amount of operation necessary for adjusting a phase difference ϕ DG  to be given to the gate signal V gs  based on an amount of ripples (affected component of V rip  shown in  FIG.  4   ) included in the output detection value of the high-frequency AC output V RF , for instance, so as to issue an output command of the gate signal V gs  including the phase difference ϕ DG  to the gate signal generation circuit  136 . Then, the gate signal generation circuit  136  generates and outputs gate signals V gs A to V gs B′ to be input to the FET elements  122 A to  122 B′ after the phase difference is set according to the amount of operation obtained from the error calculation control unit  134 . 
       FIG.  2    is a circuit diagram showing an equivalent connection circuit of the high-frequency amplifier shown in  FIG.  1   . As shown in  FIG.  2   , the high-frequency amplifier  120  in  FIG.  1    consists of, as an example, a so-called full-bridge circuit  122  by use of four FET elements  122 A,  122 A′,  122 B and  122 B′, a coil  124  connected to one of the outputs of the full-bridge circuit  122 , a transformer  126  connected on an output part of the full-bridge circuit  122 , and a capacitor  128  connected on an output part of the transformer  126 . In addition to that, the coil  124  and the capacitor  128  serve as high-frequency filters. The capacitor  128  may be arranged on an input part of the transformer. Furthermore, the coil  124  may be a wiring inductance as long as it looks like a lagging load (inductive load). 
     The full-bridge circuit  122  is configured in such a way that the DC voltage V DC  output from the AC-DC conversion unit  110  is applied directly to perform switching between four FET elements  122 A,  122 A′,  122 B and  122 B′ at a predetermined timing, thereby applying power with a predetermined polarity while two of the FET elements are being driven simultaneously. The four FET elements  122 A,  122 A′,  122 B and  122 B′ are energized when the gate voltage V gs  is applied as a gate signal to a gate electrode G, and this illustrative embodiment can present the cases where recovery loss is low even when a current of SiC-FET (silicon carbide FET), GaN-FET (gallium nitride FET) or the like flows back. 
     Next, with reference to  FIGS.  3  and  4   , a description will be made about a specific aspect of an output control method of the high-frequency power supply device according to a representative example of the present invention. 
       FIG.  3    is a time chart showing an example of the gate signals to be input to the FET elements shown in  FIG.  2   .  FIG.  4    is a waveform chart showing a relationship between an input (DC voltage) and an output (AC voltage) in the high-frequency power supply device shown in  FIG.  1   . 
       FIG.  3   (a) shows a gate signal V gs  obtained by conventional output control in a high-frequency power supply device that includes a DC-DC conversion unit. In the conventional output control, for example, gate signals V gs A and V gs B′, which are turned on simultaneously, are applied to the FET elements  122 A and  122 B′ shown in  FIG.  2   . Then, after a lapse of a predetermined dead time DT, gate signals V gs A′ and V gs B, which are turned on simultaneously, are applied to the FET elements  122 A′ and  122 B, respectively. 
     After a lapse of another dead time DT, the gate signals V gs A and V gs B′ are applied again. Consequently, the conventional output control can remove ripples by a DC-DC conversion unit, and then output a high frequency AC output V RF  in a shaded section. 
       FIG.  3   (b) shows a gate signal V gs  obtained by the output control in the high-frequency power supply device shown in  FIG.  1   . The output control according to a representative example of the invention starts inputting of gate signals V gs B and V gs B′ to the FET elements  122 B and  122 B′ at timing lagging behind start times of inputting gate signals V gs A and V gs A′ to the FET elements  122 A and  122 A′ by a phase difference ϕ DG . In this case, the difference ϕ DG  is denoted as a phase angle that can be calculated by the following Formula 1 using a residual phase ϕ DZ  caused by rated outputting and a dead time phase ϕ DT  corresponding to a dead time.  
     
       
         
           
             
               ϕ 
               
                  DG 
               
             
             = 
             
               
                 180 
               
               ∘ 
             
             − 
             
               
                 
                   ϕ 
                   
                      DZ 
                   
                 
                 + 
                 
                   ϕ 
                   
                      DT 
                   
                 
               
             
           
         
       
     
     In this context, when a period of transmitting the gate signal V gs  is T, the dead time phase ϕ DT  can be derived from the following Formula 2.  
     
       
         
           
             
               ϕ 
               
                  DT 
               
             
             = 
             
               
                 DT/ 
                 
                   
                     T/2 
                   
                 
               
             
             × 
             
               
                 180 
               
               ∘ 
             
           
         
       
     
     In the DC voltage V DC  obtained by the conversion by the AC-DC conversion unit  110 , which is the above-mentioned three-phase rectification circuit, three-phase power factor correction circuit or similar, a ripple component V rip  remains as fluctuation corresponding to the six times frequency component of commercial three-phase alternating current, as shown in  FIG.  4   . Thus, by making the above-described phase difference ϕ DG  variable according to the fluctuation of the ripple component V rip , it is possible to cancel the ripple component V rip  of the DC voltage V DC  to be input to the high-frequency amplifier  120 . Such switching control is performed on the high-frequency amplifier  120  to thereby obtain a high frequency AC output V RF  from which the ripple component V rip  is removed. 
     In general, the ripple component V rip  of the DC voltage V DC  subjected to the three-phase rectification, or conversion, in the AC-DC conversion unit  110  is approximately 14% of an amplitude value of an AC waveform before the conversion. Thus, when an acceptable fluctuation range of the commercial three-phase AC voltage is 10%, it is preferable to ensure the residual phase ϕ DZ  according to the above Formula 1 to be at least 30°. 
     In this way, as shown in  FIG.  3   (b), if the residual phase ϕ DZ  and the dead time phase ϕ DT  are made as small as possible and the phase differences ϕ DG  between the gate signals V gs A and V gs A′ as well as signals V gs B and V gs B′ are made as large as possible, the overlapping portion between them becomes large, so that the amplitude value of the high frequency AC output V RF  that will be the final output can be made larger. On the other hand, as described above, since it is necessary to ensure that the residual phase ϕ DZ  is 30° or more in order to cancel the ripple component V rip  of the DC voltage V DC  to be input to the high-frequency amplifier  120 , the adjustable range of the phase difference ϕ DG  is narrow even if the dead time DT can be minimized. Thus, in order to stably obtain the rated output, it is required to consider devising of design of the transformer  126  shown in  FIG.  2   . 
     The above-described control method enables to remove the ripple component contained in the DC voltage output from the AC-DC conversion unit without using a DC-DC conversion unit as with the conventional high-frequency power source. Thus, no DC-DC conversion unit and LC filter included in the conversion unit are needed, and thereby a response frequency of a feedback control loop is not limited with respect to the high-frequency amplifier, i.e. not limited to be one-tenth of an output frequency of the LC filter. It is therefore possible to increase a response speed of an AC voltage that will be eventually output (e.g., about 10 times faster than before). 
       FIG.  5    is a block diagram schematically showing a high-frequency power supply device according to a variation of the present invention. As shown in  FIG.  5   , a high-frequency power supply device  100  according to the variation includes the AC-DC conversion unit  110  shown in  FIG.  1   , a plurality of high-frequency amplifiers  120 , a phase conversion circuit  130  connected to the plurality of high-frequency amplifiers  120 , and an output synthesizing unit  140  arranged on output parts of the plurality of high-frequency amplifiers  120 . More specifically, the high-frequency power supply device  100  according to the variation has the plurality of high-frequency amplifiers  120  arranged in parallel, each of the high-frequency amplifiers  120  being provided with one (single) phase conversion circuit  130  so as to be subjected to the output control. 
     The plurality of high-frequency amplifiers  120  is directly supplied with a DC voltage V DC  output from the AC-DC conversion unit  110 , and each of amplifiers independently outputs high frequency AC outputs V RF1  and V RF2 . In this case, since the high-frequency amplifiers  120  are supplied with identical gate signals V gs A to V gs B′ from the phase conversion circuit  130 , it is possible to derive AC outputs V PF1  and V RF2  in which ripples are removed and phases are matched in the high-frequency amplifiers. 
     The output synthesizing unit  140  is configured to synthesize the AC outputs V RF1  and V RF2  input from the plurality of high-frequency amplifiers  120  to output them as a high frequency AC output V RF . Thus, the magnitude (amplitude value) of the AC output V RF  finally obtained by synthesizing the outputs from the plurality of high-frequency amplifiers  120  can be increased. 
       FIG.  6    is a block diagram schematically showing a high-frequency power supply device according to another variation of the invention. As shown in  FIG.  6   , a high-frequency power supply device  100  according to another variation includes, as with the device shown in  FIG.  5   , an AC-DC conversion unit  110 , a plurality of high-frequency amplifiers  120 , phase conversion circuits  130  arrange for respective high-frequency amplifiers  120 , and an output synthesizing unit  140  arranged on output parts of the plurality of high-frequency amplifiers  120 . More specifically, the high-frequency power supply device  100  according to another variation has the plurality of high-frequency amplifiers  120  arranged in parallel, each of the plurality of high-frequency amplifiers  120  being provided with a phase conversion circuit  130  so as to be subjected to the output control. 
     In the high-frequency power supply device  100  with such configuration, each of the plurality of high-frequency amplifiers  120  is individually arranged together with the phase conversion circuit  130 , so that an operation of removing a ripple component V rip  in the DC voltage V DC  to be input is performed in each of the high-frequency amplifiers  120  based on the AC voltage V RF1  or V RF2 . Consequently, the ripple removal is performed in individual high-frequency amplifiers  120 , thereby enabling to enhance the effect of ripple reduction. 
     With the above configuration, the high-frequency power supply device and the output control method therefor according to the present invention can convert an input from a three-phase AC power source into a direct current and directly input it to a high-frequency amplifier, and provide a phase difference for cancelling a fluctuation component contained in the direct current to a gate signal to be input to each of a plurality of FET elements to thereby perform switching to generate high-frequency AC power. Thus, ripples caused by the conversion of the input from the three-phase AC power source into the direct current is reduced, and the output control can be performed at a high frequency band. That can achieve a response speed of the high-frequency amplifier adaptable for two-level pulse control for changing an output level of an output voltage at high speed, by way of example. Furthermore, since a DC-DC conversion unit, which is included in the conventional high-frequency power supply device, is not incorporated, the entire size of the power supply device can be reduced significantly. 
     The above embodiments are a few examples of the high-frequency power supply device and the output control method therefor of the present invention, and thus the present invention is not limited thereto. Furthermore, those skilled in the art can modify the present invention in various ways based on the gist of the invention, which modifications are not excluded from the scope of the present invention. 
     For example, the above embodiments illustrate the so-called voltage feedback control loop that adjusts the gate signals V gs A to V gs B′ to be applied to the FET elements  122 A to  122 B′ based on the output V RF  from the high-frequency amplifier  120 . However, a forward power feedback control loop for adjusting a forward wave component of a high frequency AC output V RF  to be output may be employed. Furthermore,  FIGS.  5  and  6    illustrate the variations in which two high-frequency amplifiers  120  are provided with one phase conversion circuit or separate phase conversion circuits 130. However, three or more high-frequency amplifiers  120  and the phase conversion circuit  130  may be arranged in parallel to each other. 
     Reference Signs List  
     
       
         
           
               
               
            
               
                 
                   10 
                 
                 Three-Phase AC Power Source 
               
               
                 
                   100 
                 
                 High-Frequency Power Supply Device 
               
               
                 
                   110 
                 
                 AC-DC Conversion Unit 
               
               
                 
                   120 
                 
                 High-Frequency Amplifier 
               
               
                 
                   122 
                 
                 Full-Bridge Circuit 
               
               
                   122 A, 
                   122 A′,  122 B,  122 B′ FET Element 
               
               
                 
                   124 
                 
                 Coil 
               
               
                 
                   126 
                 
                 Transformer 
               
               
                 
                   128 
                 
                 Capacitor 
               
               
                 
                   130 
                 
                 Phase Conversion Circuit 
               
               
                 
                   132 
                 
                 Output Detection Unit 
               
               
                 
                   134 
                 
                 Error Calculation Control Unit 
               
               
                 
                   136 
                 
                 Gate Signal Generation Circuit 
               
               
                 
                   138 
                 
                 Output Command 
               
               
                 
                   140 
                 
                 Output Synthesizing Unit 
               
               
                 VDC 
                 DC Voltage 
               
               
                 V RF 
 
                 AC Output 
               
               
                 V gs A, 
                 V gs A, V gs B, V gs B’ Gate Signal 
               
               
                 V rip 
 
                 Ripple Component 
               
               
                 ϕ DG 
 
                 Phase Difference 
               
               
                 ϕ DZ 
 
                 Residual Phase 
               
               
                 ϕ DT 
 
                 Dead Time Phase