News Column

Patent Issued for Matrix Converter Controlling Apparatus

July 16, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- Panasonic Corporation (Osaka, JP) has been issued patent number 8767426, according to news reporting originating out of Alexandria, Virginia, by VerticalNews editors.

The patent's inventor is Tamaoka, Shuji (Kyoto, JP).

This patent was filed on June 5, 2013 and was published online on July 1, 2014.

From the background information supplied by the inventors, news correspondents obtained the following quote: "FIG. 21 is a diagram illustrating a conventional direct conversion circuit used in a matrix converter or the like of a direct conversion scheme (also referred to as AC direct scheme) cited in a number of documents such as Patent Literature (PTL) 1.

"With the conventional direct conversion circuit illustrated in FIG. 21, AC switches S1 to S9 each of which has a breakdown voltage against both positive and negative voltage polarities are disposed as illustrated in FIG. 21.

"As illustrated in (a) in FIG. 21, each of the AC switches (S1 to S9) has a configuration having two circuits connected in series, in which diodes and insulated gate bipolar transistors (IGBT) are connected in parallel to be oriented oppositely. Alternatively, as illustrated in (b) in FIG. 21, each of the AC switches has a configuration in which two IGBTs having reverse breakdown voltage are connected in parallel to be oriented oppositely.

"The IGBT has a feature of having a high breakdown voltage with smaller conduction loss among high-current operation devices. Accordingly, in a matrix converter of the conventional directly conversion scheme (AC direct scheme), the IGBT is used as a switching element used in the AC switches. However, since the IGBT can pass through a current only unilaterally and the breakdown voltage in an opposite direction is weak, the configuration having two circuits connected in series, in which diodes and IGBTs are connected in parallel to be oriented oppositely as illustrated in (a) in FIG. 21 is generally employed. In addition, an IGBT whose reverse breakdown voltage is increased is also developed. With this, a reverse blocking IGBT in which IGBT chips are connected inversely in parallel to face each other is also used as an AC switch, as illustrated in (b) in FIG. 21.

"Meanwhile, a power switching element formed of a nitride semiconductor which differs from a power switching element of silicon series such as IGBT is under development. Techniques related to an inverter using a feature of the power switching element is disclosed by PTL 2 and so on."

Supplementing the background information on this patent, VerticalNews reporters also obtained the inventor's summary information for this patent: "Technical Problem

"However, the direct conversion circuit using the above-described IGBT has a problem described below.

"FIG. 22A is a diagram which illustrates I-V characteristics of the IGBT. FIG. 22B is a diagram which illustrates I-V characteristics of the diode.

"In the IGBT, a pn-junction is present between a collector and an emitter. With this, as illustrated in FIG. 22A, an offset voltage is generated due to the pn-junction between the collector and the emitter, irrespective of a magnitude of a current, when the IGBT passes through a current. Likewise, as illustrated in FIG. 22B, in the diode, an offset voltage is generated in a VF voltage irrespective of a magnitude of a current.

"Accordingly, in the case of the AC switch illustrated in (a) in FIG. 21, conductive loss constantly occurs due to pn-junction offset voltages in both of the diode and the IGBT, irrespective of the magnitude of a current flowing through the switch. In addition, in the case of the AC switch illustrated in (b) in FIG. 21 as well, the conductive loss occurs due to the pn-junction offset voltage in the IGBT.

"As a result, when a direct conversion circuit of a matrix converter is configured with an AC switch using the IGBT and the diode, there is a lower limit in the loss of the direct conversion circuit even in a region where a current flowing through the AC switch is small. This results in restriction on the lower limit of the power consumption of the matrix converter, and an upper limit is posed on the efficiency which indicates the ratio of output power with respect to input power.

"In addition, a tail current passes through in the IGBT at the time of turnoff behavior of the IGBT due to an accumulation effect of a minority carrier. This deteriorates the switching loss at the time of turnoff. In the diode, a recovery current due to the accumulation effect of a minority carrier in the diode deteriorates the switching loss at the time of turnoff behavior of the IGBT. As a result, in the AC switches illustrated in (a) and (b) in FIG. 21, there is a lower limit in the switching loss. When these AC switches are used to configure a direct conversion circuit of a matrix converter, the switching loss has harmful effects on power consumption and efficiency of the matrix converter.

"It is to be noted that the above-described PTL 2 merely discloses the technique which uses a nitride semiconductor as an inverter, and thus PTL 2 is not related to a matrix converter.

"In view of the above, an object of the present disclosure is to provide a matrix converter control apparatus which is capable of reducing the loss and improve the efficiency.

"Solution to Problem

"In order to achieve the above described object, a direct conversion circuit according to an aspect of the present disclosure is a direct conversion circuit for converting a three-phase alternating current (AC) signal to a single-phase AC signal using pulse width modulation (PWM), wherein the direct conversion circuit includes: three AC input terminals to which the three-phase AC signal is supplied; six gate signal input terminals to which six gate signals are provided; an output terminal for outputting the single-phase AC signal; and three AC switches each of which is connected between a corresponding one of the three AC input terminals and the output terminal, each of the three AC switches includes a first switching element and a second switching element connected in series between the corresponding AC input terminal and the output terminal, each of the first switching element and the second switching element includes a first terminal, a second terminal, and a gate terminal, and: passes a current from the first terminal to the second terminal or from the second terminal to the first terminal, according to a polarity of a voltage applied between the first terminal and the second terminal when a first voltage is higher than a threshold voltage, the first voltage being a voltage of the gate terminal with reference to a voltage of the first terminal; interrupts a current flowing from the second terminal to the first terminal when the first voltage is lower than or equal to the threshold voltage; and passes a current from the first terminal to the second terminal when the first voltage is lower than or equal to the threshold voltage and the voltage of the gate terminal is higher than or equal to the threshold voltage with reference to a voltage of the second terminal, the direct conversion circuit further includes six pre-drive circuits each of which (i) corresponds to a different pair of corresponding ones of six gate signals and the six switching elements, and (ii) supplies a voltage between the first terminal and the gate terminal of the switching element of the corresponding pair according to the gate signal of the corresponding pair, the six switching elements being included in the three AC switches.

"According to the above-described configuration, with the direct conversion circuit according to an aspect of the present disclosure, an offset voltage due to the pn-junction as in the IGBT is not generated in the first voltage when a current is passed between the first terminal and the second terminal in the switching element used in the AC switch. With this, it is possible to reduce the conduction loss in the switching element. In addition, the AC switch does not have to include a diode, the offset voltage due to the diode is not generated, either. With this, it is possible to reduce the conduction loss in the switching element. In addition, with the reduction of the diodes, it is possible to implement reduction in the number of components, the costs, and the size of the direct conversion circuit. As described above, the direct conversion circuit according to an aspect of the present disclosure is capable of reducing the loss and improving the efficiency.

"In addition, the second terminal of the first switching element and the second terminal of the second switching element may be connected to each other, the first terminal of the first switching element may be connected to the output terminal, and the first terminal of the second switching element may be connected to the AC input terminal.

"In addition, the first terminal of the first switching element and the first terminal of the second switching element may be connected to each other, the second terminal of the first switching element may be connected to the output terminal, and the second terminal of the second switching element may be connected to the AC input terminal.

"In addition, each of the first switching element and the second switching element may include: a semiconductor stacked body including a nitride semiconductor formed on a semiconductor substrate; a first electrode and a second electrode formed, spaced from each other, on the semiconductor stacked body, the first electrode and the second electrode serving as the first terminal and the second terminal, respectively; and a gate electrode formed between the first electrode and the second electrode, the gate electrode serving as the gate terminal.

"According to the above-described configuration, the direct conversion circuit according to an aspect of the present disclosure is capable of reducing the effect of minority carrier of the switching element. With this, in the switching element, a tail current at the time of turnoff that exists in the IGBT is barely generated. Therefore, the direct conversion circuit is capable of further reducing the switching loss. In addition, the AC switch can eliminate the effect of switching loss due to a diode recovery current.

"In addition, each of the three switching elements may include: a semiconductor stacked body including a nitride semiconductor formed on a semiconductor substrate; a first electrode and a second electrode, spaced from each other, formed on the semiconductor stacked body, the first electrode and the second electrode serving as the first terminal of the first switching element and the first terminal of the second switching element, respectively; and two gate electrodes formed between the first electrode and the second electrode, each of the gate electrodes serving as the gate terminal of a corresponding one of the first switching element and the second switching element.

"According to the above-described configuration, in the direct conversion circuit according to an aspect of the present disclosure, the AC switch can be formed by a single semiconductor chip, and thus it is possible to reduce the size of the AC switch. As a result, it is possible to further reduce the size of the direct conversion circuit.

"In addition, the switching element may be a metal-oxide semiconductor field-effect transistor (MOSFET).

"In addition, a matrix converter control apparatus according to an aspect of the present disclosure may be a matrix converter control apparatus for converting a three-phase alternating current (AC) signal to a single-phase AC signal using pulse width modulation (PWM), the matrix converter control apparatus may include a matrix converter which includes the direct conversion circuit, and a PWM control unit configured to generate a PWM control signal from which the six gate signals are generated, and supply the generated PWM control signal to the matrix converter.

"According to the above-described configuration, the matrix converter control apparatus according to an aspect of the present disclosure can implement the matrix converter operation of three-phase AC to single-phase PWM which properly drives the above-described direct conversion circuit.

"In addition, the matrix converter control apparatus may further include an input voltage detecting circuit which detects a voltage value of each phase of the three-phase AC signal, the matrix converter may further include a drive control unit configured to (i) control the direct conversion circuit by generating the six gate signals using the PWM control signal, (ii) at predetermined intervals, determine, based on a result of detection performed by the input voltage detecting circuit, a first phase signal which is a signal of a phase in which a voltage has a highest absolute value in the three-phase AC signal, a second phase signal which is a signal other than the first phase signal in the three-phase AC signal, and a third phase signal which is a signal other than the first phase signal and the second phase signal in the three-phase AC signal, (iii) put a third AC switch into an interruption state, the third AC switch being one of the three AC switches to which the third phase signal is supplied via the AC input terminal, and (iv) generate the single-phase AC signal using a first AC switch and a second AC switch, the first AC switch being one of the three AC switches to which the first phase signal is supplied via the AC input terminal, and the second AC switch being one of the three AC switches to which the second phase signal is supplied via the AC input terminal.

"According to the above-described configuration, it is possible, for example, to easily perform system change to the matrix converter control apparatus from the driving system of a conventionally existing half bridge PWM inverter control apparatus which extracts AC power of an arbitrary frequency from a DC power.

"In addition, the drive control unit may switch a signal to be determined as the second phase signal alternately between the signals of two phases other than the first phase signal.

"In addition, the input voltage detecting circuit may generate a PWM output correcting signal indicating an absolute value of a difference between the first phase signal and the second phase signal, the matrix converter control apparatus may further include a PWM gain correcting circuit which generates a PWM gain correcting signal for correcting the PWM control signal according to the PWM output correcting signal to cause the single-phase AC signal generated by the direct conversion circuit to approximate the single-phase AC signal generated when the absolute value of the difference is constant, and the PWM control unit may correct a duty of the PWM control signal according to the PWM gain correcting signal.

"According to the above-described configuration, the matrix converter control apparatus according to an aspect of the present disclosure is capable of more accurately extracting an AC power of an arbitrary frequency from the three-phase AC power.

"In addition, a matrix converter control apparatus according to an aspect of the present disclosure is a matrix converter control apparatus for converting a three-phase alternating current (AC) signal to a two-phase AC signal using pulse width modulation (PWM), the matrix convertor control apparatus may include a first matrix converter and a second matrix converter each of which includes a direct conversion circuit; and a PWM control unit, wherein the PWM control unit may generate a first PWM control signal from which the six gate signals of the direct conversion circuit included in the first matrix converter are generated, supply the generated first PWM control signal to the first matrix converter, generate a second PWM control signal from which the six gate signals of the direct conversion circuit included in the second matrix converter are generated, and supply the generated second PWM control signal to the second matrix converter.

"According to the above-described configuration, the matrix converter control apparatus according to an aspect of the present disclosure can implement the matrix converter operation of three-phase AC to two-phase PWM which properly drives the above-described direct conversion circuit.

"In addition, a matrix convertor control apparatus according to an aspect of the present disclosure is a matrix convertor control apparatus for converting a three-phase alternating current (AC) input signal to a three-phase AC output signal using pulse width modulation (PWM), the matrix convertor control apparatus including: a first matrix converter, a second matrix converter, and a third matrix converter each of which includes the direct conversion circuit; and a PWM control unit, wherein the PWM control unit may generate a first PWM control signal from which the six gate signals of the direct conversion circuit included in the first matrix converter are generated, supply the generated first PWM control signal to the first matrix converter, generate a second PWM control signal from which the six gate signals of the direct conversion circuit included in the second matrix converter are generated, and supply the generated second PWM control signal to the second matrix converter, generate a third PWM control signal from which the six gate signals of the direct conversion circuit included in the third matrix converter are generated, and supply the generated third PWM control signal to the third matrix converter.

"According to the above-described configuration, the matrix converter control apparatus according to an aspect of the present disclosure can implement the matrix converter operation of three-phase AC to three-phase PWM which properly drives the above-described direct conversion circuit.

"It is to be noted that the present disclosure can be embodied not only as a direct conversion circuit and a matrix converter controlling apparatus but also a method of driving the direct conversion circuit having, as steps, the characteristic units included in the matrix converter controlling apparatus or a method of controlling the matrix converter, or as a program which causes a computer to execute such characteristic steps. In addition, it should be understood that such a program can be distributed via a non-transitory computer readable recording medium such as a CD-ROM and a transmission medium such as the Internet.

"Furthermore, the present disclosure can be embodied as a semiconductor integrated circuit (LSI) which implements part or all of the functions of the direct conversion circuit or the matrix converter controlling apparatus.

"Advantageous Effects

"The present disclosure can provide a direct conversion circuit and a matrix converter controlling apparatus which can reduce the loss and improve the efficiency."

For the URL and additional information on this patent, see: Tamaoka, Shuji. Matrix Converter Controlling Apparatus. U.S. Patent Number 8767426, filed June 5, 2013, and published online on July 1, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8767426.PN.&OS=PN/8767426RS=PN/8767426

Keywords for this news article include: Electronics, Semiconductor, Panasonic Corporation.

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC


For more stories covering the world of technology, please see HispanicBusiness' Tech Channel



Source: Electronics Newsweekly


Story Tools






HispanicBusiness.com Facebook Linkedin Twitter RSS Feed Email Alerts & Newsletters