The present invention relates to a multilevel power conversion circuit, and particularly to a circuit technique and device for adjusting voltage of a flying capacitor in a flying capacitor circuit-type multilevel power conversion circuit.
Generally, power conversion circuits in power conversion devices are two-level power conversion circuits capable of outputting a binary (two-valued) voltage.
Two-level power conversion circuits have the following three problems. A first problem is that an output voltage includes a lot of harmonics, which gives rise to a need for a large harmonic filter for outputting a favorable alternating or direct current including a low amount of harmonic components. A second problem is that a lot of electromagnetic noise is generated upon switching. A third problem is that a switching loss is high, which limits the degree to which the efficiency can be improved.
To solve the above-described problems of the two-level power conversion circuits, research and development is being made into multilevel power conversion circuits capable of outputting a ternary (three-valued) or higher voltage, and practical use of such circuits has been started in some sectors. With multilevel power conversion circuits, a voltage waveform to be output can be a truer alternating current or a truer direct current, as the number of levels is greater. Therefore, they can use a harmonic filter smaller than that in two-level power conversion circuits. Furthermore, they can suppress electromagnetic noise and switching loss, because a voltage to be applied per switching element of a main circuit is low.
Meanwhile, multilevel power conversion circuits have a problem in terms of capacitor voltage control. Multilevel power conversion circuits need to be controlled such that voltages of capacitors for synthesizing an output voltage are maintained to specific values. If the voltages of the capacitors depart from the specific values, various problems occur such as distortion of the output waveform, growth of electromagnetic noise, destruction of a main semiconductor switch of a main circuit, and destruction of the capacitors themselves.
The problem of element or capacitor destruction is particularly critical in one-chip integrated circuits. One-chip integrated circuits are circuits obtained by integrating a plurality of semiconductor elements and passive components over an insulating substrate or a semiconductor substrate through a semiconductor process. Because it is impossible to replace the elements on the one-chip integrated circuits individually, it is necessary to replace the entire integrated circuit when one element is destroyed.
Some circuit types have been proposed for multilevel power conversion circuits, including a flying capacitor circuit type, a diode clamping circuit type, and a cascaded H-bridge circuit type, for example.
The problems of the multilevel power conversion circuits described above will be described below specifically, by taking a flying capacitor circuit type for example. A flying capacitor circuit type is a multilevel power conversion circuit configured to add or subtract voltages of a plurality of flying capacitors by controlling main semiconductor switches, to thereby enable a ternary (three-valued) or higher voltage to be output.
As shown in
Here, it is required that a voltage Vn of a flying capacitor Cn having an n-th highest voltage be maintained to a prescribed value represented by the formula (1) below.
V
n
=V
IN×(N−n−1)/(N−1) (1)
N is an integer of 3 or greater representing the number of levels, n is an integer of from 1 to N−2, and VIN is an input voltage.
In an ideal flying capacitor circuit-type multilevel power conversion circuit in which all main semiconductor switches in the main circuit 2 have completely the same characteristics, and there are no parasitic inductances or parasitic capacitances in the circuit, each flying capacitor can be charged and discharged uniformly according to a common control signal generation method of comparing a plurality of carrier waves having different phases corresponding to the number of levels with a modulating wave. Hence, the voltage of each flying capacitor becomes constant at the prescribed value represented by the formula (1).
The principle behind this will be described below, using a three-level flying capacitor circuit-type multilevel power conversion circuit shown in
A three-level multilevel power conversion circuit includes only one flying capacitor, which, in
A case of three levels was described above simply as an example. When the number of levels is four or greater, there are operation modes in which charging and discharging are performed through a plurality of flying capacitors. However, as in the case of three levels, the voltages of the flying capacitors become constant at the prescribed values in principle.
However, power conversion circuits actually used have variations in the characteristics of the main semiconductor switches, and include parasitic elements in the circuit such as a parasitic resistance, a parasitic capacity, and a parasitic inductance. This causes variations in the switching time of the main semiconductor switches of the main circuit, and in the delay of a control signal, and this in turns causes a flying capacitor to be charged and discharged to different quantities contrary to the case of the ideal conditions, to make the voltage of the flying capacitor fluctuate from the prescribed value described above.
A method for overcoming this problem and maintaining the voltages of the flying capacitors at the prescribed values is disclosed in, for example, NPL 1. The method of NPL 1 detects the voltages of the flying capacitors, and charges or discharges the flying capacitors by controlling the main semiconductor switches based on the detected voltages, to thereby adjust the voltages of the flying capacitors to the prescribed values. However, with this method, numerous voltage sensors must be prepared in conjunction with increase in the number of levels, which is infeasible in terms of the volume and cost of the conversion device. Further, as the number of levels is increased, the number of operation modes of the circuit increases exponentially, and it is practically impossible for one operation mode to be selected from among these operation modes based on the voltages of the respective flying capacitors.
An object of the present invention is to provide a flying capacitor circuit-type multilevel power conversion circuit that adjusts voltages of flying capacitors to prescribed values automatically without detecting voltages of the flying capacitors.
The present invention provides a flying capacitor circuit-type multilevel power conversion circuit that adjust voltages of flying capacitors to prescribed values automatically without detecting voltages of the flying capacitors. Specifically, the problems described above will be overcome by providing a multilevel power conversion circuit and device described below.
(1) A flying capacitor circuit-type multilevel power conversion circuit, including at least: one or more flying capacitors; four or more main semiconductor switches; and an input terminal and an output terminal of a main circuit,
wherein the one or more flying capacitors are connected sequentially between:
a node between adjoining ones of the main semiconductor switches included in a first serial switch line formed by two or more of the main semiconductor switches being connected in series with one side of the input terminal; and
a node between adjoining ones of the main semiconductor switches included in a second serial switch line formed by the same number of the main semiconductor switches being connected in series with the other side of the input terminal,
wherein the output terminal of the main circuit is a node to which open terminals of the first serial switch element line and second serial switch element line are connected,
wherein the main circuit is further provided with a closed circuit composed of a resistor, and
wherein in all charging and discharging operation modes in which an output current flows through the one or more flying capacitors, the multilevel power conversion circuit has a function of adjusting voltages of the one or more flying capacitors to prescribed values automatically without detecting voltage values of the one or more flying capacitors, by letting a charging current and a discharging current of the one or more flying capacitors flow through the resistor of the closed circuit.
(2) The multilevel power conversion circuit,
wherein all of the main semiconductor switches included in the first serial switch line, or all of the main semiconductor switches included in the second serial switch line, or both thereof are produced on one substrate made of a semiconductor or an insulating material.
(3) The multilevel power conversion circuit,
wherein the resistor is connected between the output terminal of the main circuit and an output terminal of a load connected to the output terminal of the main circuit.
(4) The multilevel power conversion circuit,
wherein the resistor is connected to the output terminal of the main circuit, and to either side of the input terminal.
(5) The multilevel power conversion circuit,
wherein the resistor is connected to the output terminal of the main circuit, and to any middle point between of a plurality of input power supplies connected in series with the input terminal of the main circuit.
(6) The multilevel power conversion circuit,
wherein the resistor is composed of two or more resistors connected in series, and nodes between adjoining ones of the resistors are connected to the nodes between adjoining ones of the main semiconductor switches.
(7) The multilevel power conversion circuit,
wherein the resistor is connected in parallel with all of the main semiconductor switches of the first serial switch line or the second serial switch line.
(8) The multilevel power conversion circuit,
wherein the resistor is connected in parallel with all of the main semiconductor switches of the first serial switch line and the second serial switch line.
wherein all of the resistors have a same resistance value.
(10) The multilevel power conversion circuit according to (1) to (9), further including in the closed circuit:
a semiconductor switch connected in series with the resistor.
(11) The multilevel power conversion circuit according to (1) to (9), further including in the closed circuit:
a capacitor connected in series with the resistor.
(12) The multilevel power conversion circuit according to (1) to (11), further including in the closed circuit:
a capacitor connected in parallel with the resistor.
(13) The multilevel power conversion circuit according to (1) to (12),
wherein the resistor is a semiconductor transistor, and a gate terminal and a drain terminal of the semiconductor transistor are short-circuited.
(14) The multilevel power conversion circuit according to (1) to (13),
wherein the resistor is a semiconductor bidirectional switch.
(15) An AC-DC power conversion circuit,
wherein the AC-DC power conversion circuit is constructed by replacing the load and the input power supply of the multilevel power conversion circuit according to (1) to (14) with an alternating-current input power supply and a load, respectively.
(16) A multilevel power conversion device, including:
the multilevel power conversion circuit according to (1) to (14).
(17) An AC-DC power conversion device, including:
the AC-DC power conversion circuit according to (15).
The present invention can provide a flying capacitor circuit-type multilevel power conversion circuit with a function of adjusting voltages of flying capacitors to prescribed values without detecting voltage values of the flying capacitors. This makes it possible to adjust the voltages of the flying capacitors to the prescribed values at a higher speed than by a conventional art that needs to detect the voltage values of the flying capacitors. Furthermore, a multilevel power conversion device using this circuit can be reduced in loss, noise, production cost, and device size, and can be improved in reliability.
According to (2) described above, a multilevel power conversion circuit of which main semiconductor switches are one-chip-integrated can be prevented from element destruction, and a multilevel power conversion device using this circuit can be improved in reliability significantly.
According to (3) described above, the function of adjusting the voltages of the flying capacitors to the prescribed values can be obtained irrespective of the destinations to which the output terminal of the load is connected. Therefore, versatility of a multilevel power conversion device using this circuit can be enhanced, and the production cost of the device can be reduced yet more.
According to (4) described above, the resistor can be disposed immediately closely to the main semiconductor switches irrespective of the shape and dimension of the load. This makes it possible to suppress a parasitic inductance in the closed circuit, which leads to an effect that the voltages of the flying capacitors are adjusted to the prescribed values at a higher speed.
According to (5) described above, the effects of (3) and (4) described above can be obtained at the same time, which leads to a high versatility, a low cost, and an effect that the voltages of the flying capacitors are adjusted to the prescribed values at a high speed.
According to (6) described above, trade-off between the electricity consumed by the resistor in the closed circuit and the capability of adjusting the voltages of the flying capacitors to the prescribed values is mitigated, which makes it possible to suppress the electricity to be consumed by the resistor.
According to (7) described above, in addition to the effect of (6) described above, it is possible to design the levels of adjusting currents for adjusting the gaps from the prescribed values for each of the flying capacitors independently. Therefore, the trade-off of the capability of adjusting the voltages of the flying capacitors to the prescribed values is mitigated yet more, and the electricity to be consumed by the resistor can be suppressed.
According to (8) described above, in addition to the effect of (7) described above, it is possible to design the levels of adjusting currents for charging and discharging the flying capacitors independently. Therefore, the trade-off of the capability of adjusting the voltages of the flying capacitors to the prescribed values is mitigated yet more, and the electricity to be consumed by the resistor can be suppressed.
According to (9) described above, versatility of the circuit is enhanced, and a highly versatile multilevel power conversion circuit that can be used for various purposes can be realized. Therefore, versatility of a multilevel power conversion device using this circuit is enhanced, and the production cost of the device can be suppressed.
According to (10) described above, it is possible to open the closed circuit and interrupt a current to thereby suppress unnecessary loss in the resistor, in the case where the voltages of the flying capacitors are stable, or in an operation mode in which there is a risk that a current may flow through the resistor aside from the purpose of adjusting the voltages.
According to (11) described above, in addition to a similar effect to that of (10) described above, it is possible to interrupt a current in the closed circuit automatically without a control, which makes it possible to interrupt a current to flow through the closed circuit automatically at a high speed.
According to (12) described above, trade-off between the electricity consumed by the resistor in the closed circuit and the capability of adjusting the voltages of the flying capacitors to the prescribed values is mitigated, which makes it possible to suppress the electricity to be consumed by the resistor.
According to (13) described above, trade-off between the electricity consumed by the resistor in the closed circuit and the capability of adjusting the voltages of the flying capacitors to the prescribed values is mitigated, which makes it possible to suppress the electricity to be consumed by the resistor.
According to (14) described above, trade-off between the electricity consumed by the resistor in the closed circuit and the capability of adjusting the voltages of the flying capacitors to the prescribed values is mitigated, which makes it possible to suppress the electricity to be consumed by the resistor.
According to (15) described above, the present invention can be applied to an AC-DC power conversion circuit.
According to (16) described above, the present invention can be applied to a multilevel power conversion device.
According to (17) described above, the present invention can be applied to an AC-DC power conversion device.
In the following, a mode for carrying out the present invention (hereinafter, embodiment) will be described first. Next, results of virtual experiments using simulation will be presented in Example 1 and Example 2. Further, results of measurement using an actual device will be presented in example 3.
In the present embodiment, a flying capacitor circuit-type multilevel power conversion circuit of the present invention, as a DC-DC power conversion circuit used in a DC-DC power conversion device (of which input and output are direct currents), and a DC-AC power conversion circuit used in a DC-AC power conversion device (of which input is a direct current, and of which output is an alternating current) will be described.
The configuration of the multilevel power conversion circuit of the present invention will be described more specifically, in comparison with a three-level multilevel power conversion circuit of a conventional art shown in
More specifically, it is possible to obtain a function of adjusting the voltage to the prescribed value represented by V1=0.5×VIN, which is a result of assigning N=3 and n=1 to the formula (1) above. Hence, it is possible to realize a high-speed voltage adjustment that keeps up with fluctuations of the flying capacitor voltage. It is possible to adjust the voltage of the flying capacitor to the prescribed value at a higher speed than by a conventional art that requires detection of the voltage value of the flying capacitor. Furthermore, it is possible to suppress loss, noise, production cost, and device size of, and improve reliability of a multilevel power conversion device using this circuit.
As a more generalized circuit configuration,
As the circuit configuration, the N-level multilevel power conversion circuit of the present invention is a flying capacitor circuit-type multilevel power conversion circuit that includes at least: a flying capacitor circuit 3 composed of one or more flying capacitors 11 to 15; a main circuit 2 composed of the flying capacitor 3, four or more main semiconductor switches 21 to 30, and a main circuit output terminal 9; an input power supply 1; and a load 5 connected to the output terminal 9 of the main circuit, as shown in
Here, the prescribed value Vn of the voltage of a flying capacitor Cn having an n-th highest voltage is a value represented by the formula (2) below.
V
n
=V
IN×(N−n−1)/(N−1) (2)
N is an integer of 3 or greater representing the number of levels, n is an integer of from 1 to N−2, and VIN is an input voltage.
The voltage adjusting circuit 4 is composed of the adjusting resistor 41. The adjusting resistor 41 may be a metallic, ceramic, or semiconductor resistor. For example, it may be a wire wound resistor or a chip resistor.
The main semiconductor switches 21 to 30 constituting the main circuit 2 may be semiconductor switches having reverse conductivity. For example, as shown in
The flying capacitors 11 to 15 constituting the flying capacitor circuit 3 may be various types of capacitors. For example, they may be a ceramic capacitor using a dielectric material, a plastic film capacitor, various types of electrolytic capacitors such as an aluminum electrolytic capacitor, and a capacitor utilizing a semiconductor PN junction capacity.
The output terminal 42 of the voltage adjusting circuit can be connected as below. First, as shown in
Further, as shown in
Further, as shown in
For example, as shown in
In the present embodiment, a circuit configuration for only one phase is described for simplicity. However, in a circuit configuration having a plurality of phases, the output terminal may be connected to an output terminal of a load of other phases, etc.
In the multilevel power conversion circuit of the present invention, there is a trade-off relationship between the electricity to be consumed by the voltage adjusting circuit 4 (hereinafter, an adjusting electricity), and the capability of adjusting the voltages of the flying capacitors to the prescribed values (hereinafter, an adjusting capability). Specifically, as the resistance value of the adjusting resistor 41 is lowered, the adjusting capability increases to bring the voltages of the flying capacitors more closely to the prescribed values, but the adjusting electricity increases at the same time.
As a method for mitigating this trade-off relationship, it is possible to replace the adjusting resistor 41 constituting the voltage adjusting circuit 4 with a semiconductor element. In a normal resistor, a current changes linearly with respect to an applied voltage. With a semiconductor element, a current increases super-linearly with respect to changes of a voltage, which enables mitigation of the trade-off relationship. Further, replacement with a semiconductor element enables not only mitigation of the trade-off, but also improvement of the reliability of the device, and reduction of the size and cost of the device.
Specifically, in a DC-DC power conversion circuit, the adjusting resistor 41 may be replaced with a diode, a zener diode, a field effect transistor of which gate terminal and of which drain terminal are short-circuited, or a bipolar transistor of which base terminal and of which collector terminal are short-circuited. This makes it possible to mitigate the trade-off between the adjusting capability and the adjusting electricity.
Further, in a DC-AC power conversion circuit and an AC-DC power conversion circuit, the adjusting resistor 41 may be replaced with diodes or zener diodes of which anodes or of which cathodes are connected in series. Further, it may be replaced with an antiparallel circuit of diodes or of zener diodes, an anode of one of which and a cathode of another of which are connected. It may be replaced with an adjusting bidirectional switch obtained by connecting in series, sources or drains of field effect transistors, a gate terminal of each of which and a drain terminal of each of which are short-circuited. It may be replaced with an adjusting bidirectional switch obtained by connecting in series, emitters or collectors of bipolar transistors, a base terminal of each of which and a collector terminal of each of which are short-circuited.
As an example thereof,
Further, as shown in
Further, as shown in
Further, as shown in
Further, in
When there is one adjusting resistor as in
Further, an output terminal 42b of the voltage adjusting circuit of
Further, as an evolved model of
Further, as an evolved model of
As a further evolved model of
The voltage fluctuation width of the flying capacitors 11 to 15 is different depending on the characteristic of the load 5 connected to the multilevel power conversion circuit. Hence, for the purpose of optimization with respect to each individual load characteristic, the resistance values of the respective adjusting resistors 41a, 41b, and 31 to 40 of
Specifically, in an operation mode in which large charging and discharging currents flow through the load, the resistance value of an adjusting resistor through which the adjusting current flows in the instant operation mode may be set lower than the other adjusting resistors, which makes it possible to mitigate the trade-off between the adjusting electricity and the adjusting capability.
However, when a plurality of adjusting resistors are used as in
The circuit configurations of the voltage adjusting circuit 4 of
In
In
In
Further, in order to improve the reverse conductivity, it is desirable that the main semiconductor switches 21 to 30 each be composed of a transistor and a reversely connected diode, as shown in
In the case of P-channel-type transistor, note that it is necessary to connect the anode of a diode to be connected to the transistor to the drain of the transistor, and the cathode of the diode to the source of the transistor. Furthermore, the transistor may be replaced with other semiconductor transistors than MOSFET, such as MISFET (insulated gate field effect transistor), HFET (hetero-junction field effect transistor), JFET (junction-type field effect transistor), BT (bipolar transistor), and IGBT (insulated gate type bipolar transistor). Further, the main semiconductor switches 21 to 30 constituting the main circuit may be a combination of two or more kinds of the semiconductor transistors mentioned above. In
The diode to constitute the main semiconductor switches 21 to 30 may be, other than various diodes made of Si, a Schottky barrier diode and a PiN diode made of SiC or GaN, which makes it possible to suppress switching loss significantly.
In the present embodiment, a DC-DC power conversion circuit and a DC-AC power conversion circuit have been described. However, it is also possible to obtain the effect of adjusting the voltages of the flying capacitors to the prescribed values automatically in an AC-DC power conversion circuit obtained by exchanging the input and output of
In
It is possible to form the power conversion circuit of the present invention by integrating individual discrete elements on a printed circuit board, within a module, within a resin package, etc. Further, in such a case as in
In terms of the circuit range to be formed on one-chip, the main semiconductor switches 21 to 25 and the main semiconductor switches 26 to 30 may be formed on one-chip, respectively. It is desirable to form all of the main semiconductor switches 21 to 30 on one-chip. It is more desirable to form all of the main semiconductor switches 21 to 30 and all of the flying capacitors 11 to 15 on one-chip. It is also desirable to form the adjusting resistor on one-chip together with the main semiconductor switches, which enables voltage adjustment at a higher speed. With one-chip formation, they are formed on a substrate integrally and behave as one component as a whole, which makes it possible to reduce the number of parts significantly, and improve the reliability considerably. Furthermore, mass production is available with a semiconductor process, which leads to reduction of the production cost. Desirable materials for one-chip formation are Si, GaAs, and GaN.
However, with a one-chip circuit, it is impossible to replace an individual element when the voltage of a flying capacitor departs from a prescribed value and an element in the circuit is destroyed as a result. Therefore, flying capacitors according to a conventional art require replacement of the entire circuit formed on one-chip, which rejects practical use. The automatic voltage adjusting function of the present invention can prevent such element destruction and improve the reliability of the one-chip multi-level power conversion circuit significantly.
The effect of the present invention in the circuit configuration of
As calculation conditions, an input voltage was 200 V, the capacitance of the flying capacitors was 10 μF, a load was a serial circuit of a resistor having a resistance value of 30Ω and an inductor having an inductance of 80 mH, the frequency of the fundamental wave of an output was 50 Hz, a carrier frequency was 2 kHz (a switching cycle was 1 ms), a modulation factor was 1.0, and the resistance value of an adjusting resistor was 5 kΩ. Note that no adjusting resistor was provided in the circuit of the conventional art. In this virtual experiment by simulation, the main semiconductor switch S3 was switched at a switching delay of 1 μs, in order to simulate main semiconductor switches having variations in the characteristics.
The waveforms of the voltages of C1, C2, and C3 were integrated in the time domain, and the resultants were divided by the length of time of the integration, to thereby obtain average voltages V1, V2, and V3. Error voltage ratios VDn obtained by standardizing V1, V2, and V3 by the prescribed values Vn represented by the formula (2) above according to the formula (3) below are shown in
VD
n=(Vn−VDn)/VDn (3)
N is an integer of 3 or greater representing the number of levels, and n is an integer of 1 to N−2.
In the conventional art, the standardized error ratios of C1, C2, and C3 were −22.1%, −2.1%, and −36.5%, respectively. On the other hand, in the present invention, they were −8.7%, +1.0%, and −0.9% respectively, and turned out to be closer to the prescribed values.
Another simulation was performed by inserting an adjusting resistor in parallel with a load as shown in
The effect of the present invention in the circuit configuration of
As calculation conditions, an input voltage was 200 V, the capacitance of the flying capacitors was 10 μF, a load was a serial circuit of a resistor having a resistance value of 30Ω and an inductor having an inductance of 80 mH, the frequency of the fundamental wave of an output was 50 Hz, a carrier frequency was 2 kHz (a switching cycle was 1 ms), a modulation factor was 1.0, and the resistance values of adjusting resistors connected in parallel with the respective main semiconductor switches were 5 kΩ each, as in Example 1. Note that no adjusting resistor was provided in the circuit of the conventional art. In this virtual experiment by simulation, the main semiconductor switch S3 was switched at a switching delay of 1 μs, in order to simulate main semiconductor switches having variations in the characteristics.
The waveforms of the voltages of C1, C2, and C3 were integrated in the time domain, and the resultants were divided by the length of time of the integration, to thereby obtain average voltages V1, V2, and V3. Error voltage ratios VDn obtained by standardizing V1, V2, and V3 by the prescribed values Vn represented by the formula (2) above according to the formula (4) below are shown in
VD
n=(Vn−VDn)/VDn (4)
N is an integer of 3 or greater representing the number of levels, and n is an integer of 1 to N−2.
In the conventional art, the standardized error ratios of C1, C2, and C3 were −22.1%, −2.1%, and −36.5%, respectively. On the other hand, in the present invention, they were +0.5%, +1.1%, and −2.0% respectively, and turned out to be yet closer to the prescribed values.
As can be seen from comparison between
A prototype of a DC-AC power conversion device was produced, and the effect of the present invention with this device was verified by an experiment. A circuit used was a three-level flying capacitor circuit-type multilevel power conversion circuit. A circuit configuration of
As calculation conditions, an input voltage was 100 V, the capacitance of the flying capacitor was 8.2 μF, a load was a serial circuit of a resistor having a resistance value of 10Ω and an inductor having an inductance of 40 mH, the frequency of the fundamental wave of an output was 50 Hz, and a carrier frequency was 2 kHz. All of the main semiconductor switches were commercially available Si-MOSFETs of the same model number. The withstand voltage and On-resistance of the Si-MOSFETs are 600 V, and 0.19Ω, respectively. The resistance values of adjusting resistors connected in parallel with the respective main semiconductor switches were either 5 kΩ or 1 kΩ. For the sake of comparison, a power conversion device according to a conventional art in which no adjusting resistor was provided was also produced. The circuit configuration of the power conversion device of the conventional art was completely the same as that of the power conversion device of the present invention described above, except that no adjusting resistor was provided.
The waveform of the voltage of C1 was integrated in the time domain, and the resultant was divided by the length of time of the integration, to thereby obtain an average voltage V1. An error voltage ratio VDn obtained by standardizing V1 by the prescribed value Vn represented by the formula (1) above according to the formula (2) below are shown in
VD
n=(Vn−VDn)/VDn (5)
N is an integer of 3 or greater representing the number of levels, and n is an integer of 1 to N−2.
In the conventional art, the standardized error ratio of C1 was −54%. On the other hand, in the present invention, it was −26% and −2.0% at the voltage adjusting resistances of 5 kΩ and 1 kΩ, respectively. It was revealed that the flying capacitor voltages obtained by the present invention were closer to the prescribed value. It was also revealed that a lower resistance value of an adjusting resistor would result in a flying capacitor voltage closer to the prescribed value, i.e., in a higher adjusting capability.
Meanwhile, the ratio of loss attributed to the voltage adjusting circuit to the power that was input to the power conversion device was 0.22% and 1.08% at the voltage adjusting resistances of 5 kΩ and 1 kΩ, respectively. A trade-off relationship was observed that as the resistance value of an adjusting resistor was lowered, the adjusting capability improved but the adjusting electricity increased. That said, even the adjusting electricity at the adjusting resistance of 1 kΩ was only 1.08%, and the conversion efficiency of the power conversion device on the whole was 90% or higher, which was high. It was revealed that the present invention could provide a voltage adjusting circuit having a loss that was low enough for practical use.
The present invention can be applied to a motor drive device, a power supply device for photovoltaic generation and aerogeneration, a power supply device for an uninterruptible power system (UPS), a power supply device for an electronic device, etc.
Number | Date | Country | Kind |
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2012-201460 | Sep 2012 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2013/074221 | 9/9/2013 | WO | 00 |