Meidensha Corporation

Masakazu Muneshima

Kazunobu Oi

Issei Hirayama

Yasuhiro Yamamoto

Akihiro Kimura

Yu Sasaki

Shota Urushibata

Takahiro Murai

Hui Zhang

Tatsuya Kohara

Takuya Sugai

Akira Shigaki

The present invention provides a power conversion device in which an on-pulse bias voltage and a neutral-point bias voltage do not interfere with each other. A power conversion deviceof the present invention has a polarity judgment sectionthat judges a polarity of a neutral-point bias voltage Vcalculated by a neutral-point potential fluctuation suppression control sectionof a voltage command value control circuit, then on the basis of this polarity of the neutral-point bias voltage V, selects a polarity of an on-pulse bias voltage Vby an on-pulse control section. With this control, it is possible to prevent for the polarities of the neutral-point bias voltage Vand the on-pulse bias voltage Vfrom being different then prevent for the both bias voltages from interfering with each other.

Neutral-point-clamped multilevel power conversion device

A correction-term adder 1 compares a maximum value max(V*) with an absolute value of a minimum value min(V*). The correction-term adder 1 selects a signal 1&#x2212;max(V*) when the maximum value max(V*) is larger than the absolute value of the minimum value min(V*), on the other hand, selects a signal &#x2212;1&#x2212;min(V*) when the absolute value of the minimum value min(V*) is larger than the maximum value max(V*). Thereby, a signal of correction amount &#x3b1; is calculated. Moreover, the correction-term adder 1 produces a triangular-wave-shaped signal k(max(V*)+min(V*)) by multiplying a gain k by an addition signal max(V*)+min(V*) of the maximum value max(V*) and the minimum value min(V*). This triangular-wave-shaped signal k(max(V*)+min(V*)) is synchronized with the correction amount &#x3b1;. The correction-term adder 1 produces a correction amount &#x3b2; by selecting smaller one in absolute value between the triangular-wave-shaped signal k(max(V*)+min(V*)) and the correction amount &#x3b1;, and adds the correction amount &#x3b2; to the voltage command values V*, V*, V*.

Method of controlling power conversion device

A system stabilizing device disposed in a micro grid incorporates a self-supporting control unit (). The self-supporting control unit () allows a dq transforming unit () to determine an effective system voltage Vsd and an ineffective system voltage Vsq from a system voltage Vs. A fluctuation detecting unit () has differential characteristics and first-order lag characteristics, and determines the fluctuation component of the effective system voltage Vsd. This fluctuation component is multiplied by a gain in a proportional computing unit () to determine an ineffective current command I. A fluctuation detecting unit () does not have differential characteristics, but has first-order lag characteristics, and determines the fluctuation component of the ineffective system voltage Vsq. This fluctuation component is multiplied by a gain in a proportional computing unit () to determine an effective current command I. By so doing, hardware and computation load necessary for system stabilizing control during a self-supporting run can be reduced in the system stabilizing device.

System stabilizing device

A control unit of a system stabilization device uses a fluctuation detection block () to determine fluctuation components included in the active component and reactive component currents of a system current and fluctuation components included in the frequency signal and the amplitude signal of a system voltage. The high frequency cut-off of the fluctuation detection block () is set to be f; the low frequency cut-off is set to be f. The fluctuation detection block () is composed of a low-pass filter () with a time constant of T, a low-pass filter () with a time constant of T, a subtracter () which outputs the difference, between the output signals of the filter () and the filter (), and a feedback circuit () which provides feedback on the output of the subtracter () to the filters (). Thus, stability is ensured without using a current detector.

System stabilization device

A self-contained control unit of a system stabilizing device installed on a microgrid is provided with a fluctuation detecting blockA for determining a fluctuation component of the frequency of system voltage (C&#x3c9;s) and a fluctuation component of voltage amplitude of the system voltage (C|Vs|). The fluctuation detecting blockA determines the fluctuation component (C&#x3c9;s) based on a deviation between the output signal of a low-pass filterfor noise removal and the output signal of a low-pass filterfor determining a fluctuation detection time. An interference action inhibiting unitjudges whether system stabilizing control and governor control of a generator interfere with each other, based on a frequency signal &#x3c9;s and the fluctuation component C&#x3c9;s. If there is interference, the time constant of the low-pass filteris reduced to reduce the fluctuation component C&#x3c9;s, thereby decreasing the amount of control by the system stabilizing device and preventing interference. By this measure, system stabilizing control is exercised, without interfering with the governor control or AVR control of the generator.

A control unit of a system stabilizing device uses a fluctuation detecting block (A) to determine fluctuation components included in the active component and reactive component currents of a system current. The fluctuation detecting block (A) is composed of a low-pass filter () for noise removal having first order lag characteristics with a time constant of T1, a low-pass filter () for setting a fluctuation detection time having first order lag characteristics with a time constant of T2, a subtracter () which performs subtraction between the output signals of the filter () and the filter () and outputs the difference, an amplifier () for amplifying the output of the subtracter (), a rating limiter () for limiting the output of the amplifier, and an overcompensation inhibiting unit () which changes T4 to a smaller value when the rating limiter () performs a limiter action.

A control unit of a system stabilizing device uses a fluctuation detecting blockfor determining current commands from a system current. A fluctuation detecting unitdetermines, from an active component Iof the system current, a common current command Iwhich is a fluctuation component of the active component I. A first current command creating unitreceives as an input the current command I, and outputs a current command Iwhose signal width is as small as Tand which instantaneously rises and then gradually decreases. A second current command creating unitreceives as an input the current command I, and outputs a current command Iwhich gradually increases for a time Tand then gradually decreases for a time (T-T). The system stabilizing device having short charging and discharging times is controlled by the current command I, while the system stabilizing device having long charging and discharging times is controlled by the current command I, whereby system stabilizing controls can be exercised without interferences. In this manner, even if system stabilizing devices having different charging and discharging characteristics are provided, system stabilizing controls can be effected without interferences.

Growing community of inventors

Tokyo, Japan

Masakazu Muneshima