Abstract:
A pulse width modulation (PWM) control device for converting a first PWM signal for a two-level power conversion device to a second PWM signal for a three-level power conversion device, the three-level power conversion device including a switch, the second PWM signal driving the switch through a drive unit. The PWM control device includes an input terminal for receiving the first PWM signal for the two-level power conversion device, a conversion unit configured to convert the first PWM signal into the second PWM signal for the three-level power conversion device, and an output unit that outputs the second PWM signal to the drive unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2016-054144, filed on Mar. 17, 2016, the entire contents of which are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a PWM (Pulse Width Modulation) control device for a three-level power conversion device, in particular, a technology for configuring the PWM control device for the three-level power conversion device by adding a circuit that receives an output of a two-level control circuit that outputs a PWM signal for a two-level power conversion device, to the two-level control circuit. 
       BACKGROUND 
       [0003]    As a circuit system that generates a PWM signal used in a three-level power conversion device, a control circuit for a power conversion device that specializes in the three-level power conversion device and that realizes a PWM control system is known, for example, as described in the patent documents described below. 
         [0004]    Japanese Laid-Open Patent Publication No. 2006-109541 discloses a control circuit for a power converter that realizes a PWM control system in which a high-speed current control response can be made, and in which harmonics can be suppressed and a switching frequency does not change significantly, in a three-level converter. 
         [0005]    Japanese Laid-Open Patent Publication No. 2013-158093 discloses a three-level inverter in which control means for controlling each of three phases, U, V, and W, performs PWM processing by using a modulation signal λ from modulation signal generation means and a carrier signal from carrier signal generation means so as to generate a control signal that controls switching elements T 1  to T 4  of a switching leg of each of the phases. 
         [0006]    Japanese Laid-Open Patent Publication No. 2014-103748 (see, for example, paragraph 0029 and FIG. 1 therein) discloses a control circuit of a power conversion device that specializes in a multilevel inverter of three or more levels, and that realizes a PWM control system, and further discloses that a control unit for power conversion is configured by an application specific integrated circuit (ASIC) or the like. 
         [0007]    The patent documents above disclose a PWM control device that principally specializes in a three-level power conversion device. However, a PWM control device for a two-level power conversion device and a PWM control device for a three-level power conversion device are not compatible with each other, and therefore a PWM control device (a PWM signal generation device) may be individually prepared for each of the PWM control devices. 
       SUMMARY 
       [0008]    A PWM control device according to an embodiment, the PWM control device incorporating a control signal generation circuit that drives a semiconductor element that configures a three-level power conversion device, includes: a two-level control circuit that outputs a PWM signal for a two-level power conversion device; a conversion unit that converts the PWM signal that is output from the two-level control circuit into a PWM signal for the three-level power conversion device; and an output unit that outputs the converted PWM signal for the three-level power conversion device to a drive unit that drives a switch of the three-level power conversion device. 
         [0009]    In a three-level power conversion device using the PWM control device according to an embodiment, two sets of the PWM control devices are prepared in advance, the PWM signal that is output from the two-level control circuit is input to an input unit of each of the prepared two sets of the PWM control devices, a signal that is output from an output unit of each of the two sets of the PWM control devices is input to gates of four semiconductor switches via the drive units of the respective four semiconductor switches, the four semiconductor switches configuring an upper arm and a lower arm of a main circuit of the three-level power conversion device, or configuring the upper arm, the lower arm, and reverse blocking switches, and an AC (Alternating Current) signal is obtained from an output unit of the main circuit of the three-level power conversion device. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a circuit block diagram illustrating a minimum configuration of a circuit that converts a PWM signal for a two-level power conversion device into a PWM signal for a three-level power conversion device, according to an embodiment of the present invention; 
           [0011]      FIG. 2  illustrates the configuration of a main circuit  25  of a two-level power conversion device in related art; 
           [0012]      FIG. 3  illustrates the configuration of a main circuit  38  of a three-level power conversion device in related art; 
           [0013]      FIG. 4  is a first block diagram illustrating the configuration of a three-level power conversion device, which includes a circuit that converts a PWM signal for a two-level power conversion device into a PWM signal for a three-level power conversion device, according to the embodiment of the present invention; 
           [0014]      FIG. 5  is a second block diagram illustrating the configuration of a three-level power conversion device, which includes a circuit that converts a PWM signal for a two-level power conversion device into a PWM signal for a three-level power conversion device, according to the embodiment of the present invention; 
           [0015]      FIG. 6  is a third block diagram illustrating the configuration of a three-level power conversion device, which includes a circuit that converts a PWM signal for a two-level power conversion device into a PWM signal for a three-level power conversion device, according to the embodiment of the present invention; 
           [0016]      FIG. 7  illustrates a variation of the circuit illustrated in  FIG. 4  that converts a PWM signal for a two-level power conversion device into a PWM signal for a three-level power conversion device, according to the embodiment of the present invention; 
           [0017]      FIG. 8  is a waveform chart that is obtained in circuit simulation performed to explain an effect of a PWM control device according to the embodiment of the present invention; and 
           [0018]      FIG. 9  is a waveform chart illustrating a result of circuit simulation to demonstrate a PWM signal observed in  FIG. 8  by using a three-level power conversion device according to the embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0019]    An embodiment of the present invention is described below in detail. 
         [0020]      FIG. 1  is a circuit block diagram illustrating a minimum configuration of a circuit that converts a PWM signal for a two-level power conversion device into a PWM signal for a three-level power conversion device, according to the embodiment of the present invention, and  FIG. 2  illustrates the configuration of a main circuit  25  of a two-level power conversion device in related art. 
         [0021]    In  FIG. 1 , a PWM signal (illustrated in  FIG. 2  as a signal for a U-phase) that is output from a two-level control circuit  23  (see  FIG. 2 ) is input to an input unit  101  (i.e., an input terminal). A high-frequency component is removed from the signal input to the input unit  101  by using a low pass filter  102  such that a signal including only a fundamental wave component is obtained, and the obtained signal is input to a frequency divider circuit (a ½ frequency divider)  103  on a post stage. 
         [0022]    The signal including only the fundamental wave component is binarized by using a threshold of an input terminal of the frequency divider circuit  103  in the frequency divider circuit  103 , the frequency of the signal is halved, and the signal is further converted into a signal for which a phase is shifted by a delay circuit  104  on the next stage. 
         [0023]    An output signal of the delay circuit  104  and the signal input to the input unit  101  are input to an AND circuit  105 . One signal that is branched from an output of the AND circuit  105  is output from an output unit  107  (i.e., an output terminal) as a (first) output signal (for example, a drive signal of a semiconductor switch T 1  of an upper arm of a U-phase), and the other signal that is branched from the output of the AND circuit  105  is output from an output unit  108  (i.e., an output terminal) via a NOT circuit  106  as a (second) output signal (for example, a drive signal of a semiconductor switch T 3  of a lower arm of the U-phase). The AND circuit  105  and the NOT circuit  106  configure (i.e., constitute) a branching circuit, and the branching circuit configures an output unit of a PWM control device of a three-level power conversion device. 
         [0024]    Semiconductor switches in a switching leg of each phase that configures a main circuit of the three-level power conversion device are usually referred to as T 1  to T 4  from the top in many cases. 
         [0025]    As illustrated in  FIG. 2 , in a two-level power conversion device, PWM signals that are output from a two-level control circuit  23  are input, for example, to gates of a semiconductor switch  21  and a semiconductor switch  22  that configure a switching leg  24  of a U-phase of the two-level power conversion device, via a switch drive circuit  26 . The switching leg above is also prepared for each of a V-phase and a W-phase such that a three-phase two-level power conversion device is configured. The signals that are input to the gates of the semiconductor switch  21  and the semiconductor switch  22  are mutually inverted in such a way that the two semiconductor switches are not in the ON state simultaneously. As the signals are mutually inverted, a difference in a phase between both of the signals is 180 degrees. 
         [0026]      FIG. 3  illustrates the configuration of a main circuit  38  of a three-level power conversion device in related prior art. In  FIG. 3 , semiconductor switches  31  to  34  configure a switching leg for a U-phase, and the switching leg is further prepared for a V-phase and a W-phase such that a three-phase three-level power conversion device is configured. 
         [0027]    PWM signals generated by a three-level control circuit  35  illustrated in  FIG. 3  are input, for example, to gates of the semiconductor switches  31  to  34  that configure the switching leg for the U-phase via switch drive circuits  36  that drive the semiconductor switches of the U-phase. A series circuit that is configured of two diodes is connected between a connection point of the semiconductor switches  31  and  32  and a connection point of the semiconductor switches  32  and  33 , and an intermediate voltage of three levels of voltages is connected to a connection point of the two diodes. In the configuration above, when the semiconductor switches  31  and  32  are in the ON state and the semiconductor switches  33  and  34  are in the OFF state, a high voltage is output from the switching leg, and when the semiconductor switches  31  and  32  are in the OFF state and the semiconductor switches  33  and  34  are in the ON state, a low voltage is output from the switching leg. When the semiconductor switches  31  and  34  are in the OFF state and the semiconductor switches  32  and  33  are in the ON state, an intermediate voltage is output from the switching leg. 
         [0028]      FIG. 4  is a first block diagram illustrating the configuration of a three-level power conversion device that includes a circuit that converts a PWM signal for a two-level power conversion device into a PWM signal for a three-level power conversion device, according to the embodiment of the present invention. A two-level control circuit  23  and PWM signal conversion circuits  200  and  210  configure a PWM control device of the three-level power conversion device (the same hereinafter). 
         [0029]    In  FIG. 4 , a signal for an upper arm of a two-level power conversion device that is output from the two-level control circuit  23  for the two-level power conversion device is input to the PWM signal conversion circuits  200  and  210 , an output signal  201  that is output from the PWM signal conversion circuit  200  is input to a gate of a semiconductor switch  31  that configures an upper arm of a U-phase, via a switch drive circuit, and an output signal  202  that is output from the PWM signal conversion circuit  200  is input to a gate of a semiconductor switch  33  that configures a lower arm of the U-phase, via a switch drive circuit. A difference of a half cycle of an output signal of a PWM signal conversion circuit (one cycle of a fundamental wave that is output from a low pass filter  102 ) is set as delay amounts of both of delay circuits  104  that respectively configure the PWM signal conversion circuits  200  and  210 . In addition, an output signal  211  that is output from the PWM signal conversion circuit  210  is input to a gate of a semiconductor switch  34  that configures the lower arm of the U-phase, via a switch drive circuit, and an output signal  212  that is output from the PWM signal conversion circuit  210  is input to a gate of a semiconductor switch  32  that configures the upper arm of the U-phase, via a switch drive circuit. Consequently, a main circuit  37  (a switching leg) for the U-phase of a three-phase three-level power conversion device is realized. 
         [0030]    The configuration above is also prepared for each of a V-phase and a W-phase of three phases such that a main circuit  38  of the three-phase three-level power conversion device is configured. 
         [0031]      FIG. 5  is a second block diagram illustrating the configuration of a three-level power conversion device that includes a circuit that converts a PWM signal for a two-level power conversion device into a PWM signal for a three-level power conversion device, according to the embodiment of the present invention. Namely,  FIG. 5  illustrates an example in which the main circuit (the switching leg) for the U-phase of the three-level power conversion device of  FIG. 4  is applied to a T-type circuit that is configured by semiconductor switches  41  to  44 , and this configuration is also prepared for each of a V-phase and a W-phase of three phases such that a main circuit  45  of a three-level power conversion device is realized. 
         [0032]    In  FIG. 5 , the configurations of a two-level control circuit  23  and PWM signal conversion circuits  200  and  210  in a two-level power conversion device are the same as those in  FIG. 4 . In this case, an output signal  201  that is output from the PWM signal conversion circuit  200  is input to the semiconductor switch  41  that configures an upper arm of the U-phase, via a switch drive circuit, and an output signal  202  that is output from the PWM signal conversion circuit  200  is input to the semiconductor switch  42  that connects an intermediate point of the upper and lower arms of the U-phase to an intermediate voltage, via a switch drive circuit. 
         [0033]    In addition, an output signal  211  that is output from the PWM signal conversion circuit  210  is input to the semiconductor switch  44  that configures the lower arm of the U-phase, via a switch drive circuit, and an output signal  212  that is output from the PWM signal conversion circuit  210  is input to the semiconductor switch  43  that connects the intermediate point of the upper and lower arms of the U-phase to the intermediate voltage, via a switch drive circuit. Consequently, a main circuit  40  for the U-phase of a three-phase three-level power conversion device is realized. The semiconductor switches  42  and  43  configure a switch circuit that connects the intermediate point of the upper and lower arms (this is also a connection point of the semiconductor switches  41  and  42  and an output unit) to an intermediate voltage of three levels of voltages. When the semiconductor switches  41  and  42  are in the OFF state and the switch circuit above is in the ON state, the intermediate voltage is output from the U-phase. 
         [0034]    The configuration above is also prepared for the V-phase and the W-phase of the three phases such that the three-phase three-level power conversion device is configured. 
         [0035]      FIG. 6  is a third block diagram illustrating the configuration of a three-level power conversion device that includes a circuit that converts a PWM signal for a two-level power conversion device into a PWM signal for a three-level power conversion device, according to the embodiment of the present invention. Namely,  FIG. 6  illustrates an example in which the main circuit for the U-phase of the three-level power conversion device of  FIG. 4  is applied to a T-type circuit that is configured by semiconductor switches  51  to  54 , and this configuration is also prepared for each of a V-phase and a W-phase of three phases such that a three-level power conversion device is realized. The semiconductor switches  52  and  53  are reverse blocking semiconductor switches. 
         [0036]    In  FIG. 6 , the configurations of a two-level control circuit  23  and PWM signal conversion circuits  200  and  210  in a two-level power conversion device are the same as those in  FIG. 4 . In this case, an output signal  201  that is output from the PWM signal conversion circuit  200  is input to the semiconductor switch  51  that configures an upper arm of the U-phase, via a switch drive circuit, and an output signal  202  that is output from the PWM signal conversion circuit  200  is input to the semiconductor switch  52  that connects an intermediate point of the upper and lower arms of the U-phase to an intermediate voltage, via a switch drive circuit. 
         [0037]    In addition, an output signal  211  that is output from the PWM signal conversion circuit  210  is input to the semiconductor switch  54  that configures the lower arm of the U-phase, via a switch drive circuit, and an output signal  212  that is output from the PWM signal conversion circuit  210  is input to the semiconductor switch  53  that connects the intermediate point of the upper and lower arms of the U-phase to the intermediate voltage, via a switch drive circuit. Consequently, a main circuit (a switching leg)  50  for the U-phase of a three-phase three-level power conversion device is realized. The semiconductor switches  52  and  53  configure a switch circuit that connects the intermediate point of the upper and lower arms (this is also a connection point of the semiconductor switches  51  and  52  and an output circuit) to an intermediate voltage of three levels of voltages. When the semiconductor switches  51  and  52  are in the OFF state and the switch circuit above is in the ON state, the intermediate voltage is output from the U-phase. 
         [0038]    The configuration above is also prepared for each of a V-phase and a W-phase of three phases such that a main circuit of a two-phase three-level power conversion device is configured. 
         [0039]      FIG. 7  illustrates a variation of the circuit illustrated in  FIG. 4  that converts a PWM signal for a two-level power conversion device into a PWM signal for a three-level power conversion device, according to the embodiment of the present invention. Namely,  FIG. 7  illustrates an exemplary configuration in which the PWM signal conversion circuits  200  and  210  illustrated in  FIG. 4  are transformed. 
         [0040]    In  FIG. 7 , a variation  220  of a PWM signal conversion circuit is configured by adding another pair of the AND circuit and the NOT circuit in the PWM signal conversion circuit  200  illustrated in  FIG. 4  and adding a NOT circuit to one (a side that is connected to an output of a delay circuit  104 ) of the input units of the added AND circuit. The operation of the variation  200  is the same as the operation in  FIG. 4 , and could be easily understand by those skilled in the art. Therefore, the description thereof is omitted. A two-level control circuit  23  and a PWM signal conversion circuit  220  configure a PWM control device of a three-level power conversion device. 
         [0041]      FIG. 8  is a waveform chart that is obtained in circuit simulation performed to explain an effect of a PWM control device according to the embodiment of the present invention. The PWM signal conversion circuits  200  and  210  of  FIGS. 4 to 6  are target circuits in this simulation. Three waveforms of a group illustrated in the second portion from the top in  FIG. 8  indicate PWM signals for the upper arms of the U-phase, the V-phase, and the W-phase that are respectively obtained from the two-level control circuit  23  (signals for the lower arms are obtained by inverting the signals illustrated in  FIG. 8 ). A waveform of an output signal of the low pass filter  102  in the U-phase is illustrated in the uppermost portion of  FIG. 8 , together with a straight line indicating a threshold of an input terminal of the delay circuit  104 . The output signal of the low pass filter  102  is binarized by using the threshold of the input terminal, and the frequency of the output signal is halved in the frequency divider circuit  103 , and the obtained signal is further delayed by a prescribed time in the delay circuit  104  on the next stage such that obtained signal is converted into a signal for which a phase is shifted. A group in the third portion of  FIG. 8  indicates output signals of the delay circuit  104 . Three signals illustrated in the third portion of  FIG. 8  are obtained from PWM signals for the upper arms of the U-phase, the V-phase, and the W-phase that are respectively obtained from the two-level control circuit  23 . 
         [0042]    Groups illustrated in the third, fourth, and fifth portions of  FIG. 8  indicate drive signals for four switch elements (these correspond to the switch elements  31  to  34  of  FIG. 4 ) of each of the U-phase, the V-phase, and the W-phase. Four signals indicated in each of the groups respectively correspond to the signals  201 ,  211 ,  202 , and  212  illustrated in  FIGS. 4 to 6  in order from the top. It can be confirmed that the waveforms of PWM signals that are input to the main circuit  38  of the three-level power conversion device illustrated in  FIG. 4 , for example, were obtained. 
         [0043]      FIG. 9  is a waveform chart illustrating a result of circuit simulation to demonstrate a PWM signal observed in  FIG. 8  by using a three-level power conversion device according to the embodiment of the present invention. 
         [0044]    As a circuit simulation result of  FIG. 9  shows, as an example, a sine wave output (see the third from the top) is obtained as an output current waveform of the U-phase, and it can be confirmed that a signal that is equivalent to the signal of the conventional three-level control circuit illustrated in  FIG. 3  was obtained, by referencing the circuit simulation result of  FIG. 9 . Therefore, it can be confirmed that a PWM signal for a three-level power conversion device was obtained by adding a circuit that converts a PWM signal for a two-level power conversion device into a PWM signal for a three-level power conversion device according to the present invention. 
         [0045]    An operation for one of three phases, for example, the U-phase, has been described above, and description of the operations for the V-phase and the W-phase of the three phases has been omitted. However, those skilled in the art could easily understand that one two-level control circuit  23  can cope with the V-phase and the W-phase of the three phases. 
         [0046]    In addition, the delay circuit  104  of each of the phases generates a signal that is shifted from each other by an amount that corresponds to 120 degrees of an output signal cycle of a PWM signal conversion circuit (it is assumed, for example, that phase delay amounts of the delay circuit  104  of the PWM signal conversion circuit  200  or  220  of  FIGS. 4 to 7  for the U-phase, the V-phase, and the W-phase are respectively amounts that correspond to 0 degree, 120 degrees, and 240 degrees, and it is also assumed that phase delay amounts of the delay circuit  104  of the PWM signal conversion circuit  210  of  FIGS. 4 to 6  for the U-phase, the V-phase, and the W-phase are respectively amounts that correspond to 180 degrees, 300 degrees, and 60 degrees). 
         [0047]    The frequency or cycle of an output of each of the phases is a frequency obtained by halving the frequency of an output signal of the two-level control circuit  23 , or a cycle obtained by doubling the cycle of the output signal. Accordingly, it can be understood that three levels of PWM signals are generated from two levels of PWM signals, as illustrated in the lower portion of  FIG. 8 . 
         [0048]    In a case in which the two-level control circuit  23  above is provided in each of the U-phase, the V-phase, and the W-phase (namely, three two-level control circuits  23  in total are provided), the delay circuit  104  can be omitted. 
         [0049]    As described above, according to an embodiment, an existing two-level control circuit that generates a PWM signal for a two-level power conversion device does not need to be changed, and a dedicated three-level control circuit that generates a PWM signal for a three-level power conversion device does not need to be generated additionally. A PWM control device for a three-level power conversion device can be realized by adding a circuit that converts an output of the existing two-level control circuit into a PWM signal for a three-level power conversion device, to the existing two-level control circuit. 
         [0050]    Stated another way, a PWM signal for a two-level control circuit can be easily converted into a PWM signal for a three-level power conversion device only by adding a new circuit to the existing two-level control circuit. 
         [0051]    The present invention is not limited to the embodiment above, and various improvements or variations can be made without departing from the gist of the present invention.