JP5040585B2 - Power conversion system - Google Patents

Description

  The present invention relates to a power conversion system including a power conversion device, a load driven by the power conversion device, and a power source connected between a neutral point of the load and the power conversion device. The present invention relates to a technique for increasing the current utilization rate by relaxing the current duty of a semiconductor element to be configured.

Fig.5 (a) has shown the circuit structure of the three-phase inverter which is a typical example of a power converter device. In the figure, the output terminals U, V, W of the three-phase inverter constituted by semiconductor switches Q _u , Q _v , Q _w , Q _x , Q _y , Q _z made of IGBT or the like are shown by three-phase coils. A load M such as an electric motor is connected. Note that PS is a DC power source, _Cd is a DC intermediate capacitor, and the whole including them is represented as a power converter 100.

In the power conversion device 100, the semiconductor switch _{Q u, Q v, Q w} , by turning on and off the _{Q x, Q y, Q z} , DC power of any magnitude of the DC power source PS, a three-phase AC power having a frequency To be supplied to the load M. Here, FIG. 5B shows waveforms of the three-phase alternating currents i _u , i _v , i _w supplied from the power conversion apparatus 100 to the load M.

FIG. 5C shows semiconductor switches Q _u and Q _x for one phase (U phase) upper and lower arms of the three-phase inverter in FIG. 5A together with a DC intermediate capacitor C _d , and U-IGBT. , X-IGBT are switching elements (IGBTs) for the upper arm and the lower arm, respectively, and U-FWD and X-FWD are free-wheeling diodes for the upper arm and the lower arm, respectively.
When the U-phase current i _u as shown in FIG. 5B flows, a balanced current flows through each semiconductor element of FIG. 5C as shown in FIG. 5D.

Here, in the circuit of FIG. 5A, the DC power source PS is directly connected to the DC intermediate capacitor _Cd . This case, since the output of the three-phase inverter from a change in the dc voltage V _d varies, it is necessary to output control of the three-phase inverter to compensate for fluctuation of the DC voltage V _d.

FIG. 6 shows another conventional technique in consideration of the output control of the above-described three-phase inverter, and shows a power conversion device 100A in which a boost chopper Chop is added to the three-phase inverter of FIG.
The step-up chopper Chop is connected between the DC power source PS and the DC intermediate capacitor _Cd, and includes semiconductor switches Q _p and Q _n and a reactor L _c . By alternately turning on and off the semiconductor switches Q _p and Q _n , the voltage E _d of the DC intermediate capacitor C _d can be adjusted to be higher than the voltage V _{d of the} DC power source PS. For example, a battery or the like is used for the DC power source PS. even if the voltage that is suspended Te, keeping the DC intermediate voltage E _d of the three-phase inverter by the operation of the step-up chopper Chop constant, the output of the three-phase inverter can be stabilized.

Next, FIGS. 7 (a) is an art to connect the DC power supply PS between the negative electrode of the DC intermediate capacitor C _d of the neutral point and the power conversion apparatus 100B of the load M (the so-called zero-phase converter) These are described in Patent Documents 1 and 2 described later.
According to the prior art of FIG. 7A, by using the inductance of the load M and the on / off of the semiconductor switches Q _{u to} Q _z of the three-phase inverter without using the step-up chopper Chop shown in FIG. it is possible to maintain the voltage E _d of DC intermediate capacitor C _d to a value higher than the voltage V _d of the DC power supply PS.

That is, all the semiconductor switches Q _u , Q _v , and Q _w of the upper arm of the three-phase inverter are turned on (the lower arm switches Q _x , Q _y , and Q _z are all turned off), or the lower arm switches Q _x , Q are turned off. The three upper and lower arms of the three-phase inverter are equivalently operated as one upper and lower arm by a switching mode in which all _y and Q _z are turned on (all upper switches Q _u , Q _v and Q _w are turned off). A zero voltage can be output from the phase inverter.
Thereby, the boosting operation similar to that of the boosting chopper Chop in FIG. 6 can be realized by the three-phase inverter, and the output voltage and the output current can be obtained by operating the three-phase inverter in accordance with a predetermined switching pattern as in the prior art. And can be supplied to the load M.

Therefore, when the load M is, for example, an electric motor, it is possible to simultaneously driving the motor is supplied to the DC intermediate capacitor C _d boosts the DC voltage V _d. In particular, according to this prior art, the step-up chopper Chop shown in FIG. 6 is not necessary, so that the number of parts and the cost can be reduced.
Note that in FIG. 7 (a), i _d represents the current flowing into the neutral point of the load M from the DC power supply PS. FIGS. 7B to 7D are operation explanatory views of FIG. 7A, which will be described later.

Japanese Patent No. 3219039 (paragraphs [0014] to [0021], FIGS. 1 to 4 etc.) Japanese Patent No. 3223842 (paragraphs [0029], [0030], FIG. 10, FIG. 11, etc.)

FIG. 7B shows a current waveform when the conventional technique shown in FIG. 7A performs a powering operation as a three-phase inverter. The three-phase alternating current i _u , corresponding to the power supplied to the load M, is shown. i _v and i _w are supplied from the DC power source PS.
Now, when the DC current flowing from the DC power supply PS and i _d, the load M is that the direct current i _{d /} 3 to the three-phase alternating current as shown in FIG. 7 (b) flow is superimposed on the negative side Thus, the waveforms of the three-phase AC currents i _u , i _v , i _w are positive and negative and asymmetric.

FIG. 7C shows one phase (U phase) of the three-phase inverter as in FIG. 5C, and FIG. 7D shows the U-phase current i _u and FIG. 7C. The electric current which flows into each semiconductor element of is shown.
In this case, unlike FIG. 5D, the current flowing through each semiconductor element is not uniform, and the current duty of a specific semiconductor element becomes severe. For example, in the example of FIG. 7D, the current flowing through the upper-arm freewheeling diode U-FWD and the lower-arm switching element X-IGBT is larger than that of other semiconductor elements, and the loss due to heat generation also increases.

Also, as shown in FIG. 8, when the load M is in a regenerative operation, power is regenerated to the DC power source PS, and therefore, as shown in FIG. 8 (b), the three-phase alternating current is reversed in the direction opposite to FIG. 7 (b). A direct current i _d / 3 is superimposed on the positive side with respect to i _u , i _v , and i _w . In this case, as shown in FIG. 8D, the current flowing through the switching element U-IGBT of the upper arm and the freewheeling diode X-FWD of the lower arm is larger than that of other semiconductor elements.

Accordingly, a semiconductor element having a sufficient current capacity is used, or a plurality (for example, n) of semiconductor switches Q _{u1 to} Q _un , having the same current capacity for the upper and lower arms, as in the U-phase conversion unit 100C shown in FIG. Q _{x1 to} Q _xn need to be uniformly connected in parallel to reduce the current duty of each element, resulting in deterioration of the current utilization rate of the semiconductor element, increase in cost, and enlargement of the entire apparatus.

  Therefore, the problem to be solved by the present invention is to provide a power conversion system capable of increasing the current utilization rate by equalizing the current duty of the semiconductor elements constituting the power conversion device and preventing an increase in cost and an increase in the size of the entire device. There is.

In order to solve the above-mentioned problem, the invention according to claim 1 is directed to a power conversion device having a plurality of semiconductor switching elements and freewheeling diodes connected in reverse parallel to these switching elements, and to an output terminal of the power conversion device. A power conversion system comprising: a load connected to the power source connected between a neutral point of the load and a positive DC terminal or a negative DC terminal of the power converter;
The current capacity of the switching element or the freewheeling diode is changed according to a power running operation mode and a regenerative operation mode of the load.

The invention according to claim 2 is the power conversion system according to claim 1,
By changing the parallel number of the switching elements or freewheeling diodes, the current capacity of these elements is changed.

The invention according to claim 3 is the power conversion system according to claim 1 or 2,
A switch for connecting the power source between the neutral point of the load and the positive DC terminal or the negative DC terminal of the power converter according to the power running operation mode and the regenerative operation mode of the load. Is.

  According to the present invention, an element having an optimum current capacity can be used for each semiconductor element by a method such as changing the parallel number in the upper and lower arms of the semiconductor element constituting the power conversion device, and the current capacity is more than necessary. Compared with the case where semiconductor elements are uniformly connected in parallel, the current utilization rate can be improved, the cost can be reduced, and the size of the apparatus can be reduced.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, FIG. 1 shows a first embodiment of the present invention. FIG. 1A shows the overall configuration of the present embodiment, which is the same as FIG. 7A. However, as described below, semiconductor switches Q _u , Q _v , Q _w , Q _x , Q _y , configuration of Q _z is different. Note that P is a positive DC terminal of the power converter, and N is a negative DC terminal.
FIG. 1B shows the configuration of the semiconductor switches Q _u and Q _x of the upper and lower arms for one phase in FIG. 1A together with the DC intermediate capacitor C _d . The other semiconductor switches Q _v , Q _y and Q _w , Q _{z have} the same configuration as that shown in FIG.

In FIG. 1B, the upper arm semiconductor switch Q _u is configured by connecting all the m semiconductor switching elements Q _{u1 to} Q _um and the n freewheeling diodes D _{u1 to} D _un in parallel. . Here, there is a relationship of m <n with respect to the number of switching elements and freewheeling diodes (the number of parallel diodes).
On the other hand, the semiconductor switch Q _x in the lower arm is configured by connecting all the n semiconductor switching elements Q _{x1 to} Q _xn and the m _freewheeling diodes D _{x1 to} D _xm in parallel.

As described in the prior art of FIG. 7, in the circuit of FIG. 1A, the waveforms of the three-phase AC currents i _u , i _v , and i _w become asymmetrical with positive and negative by the superposition of the DC current i _d / 3. Therefore, as shown in FIG. 9, it is not necessary to arrange the same number of switching elements and freewheeling diodes symmetrically in the upper and lower arms, and the current duty per one switching element or freewheeling diode on the arm side where more current flows is reduced. Thus, there is no problem even if the numbers of the switching elements and the freewheeling diodes are made different between the upper and lower arms.

Here, FIG. 1C is a circuit for one phase (U phase) corresponding to FIG. 1B, and the switching element U-IGBT of the upper arm is the switching elements Q _{u1 to} Q of FIG. the _um, circulating diode U-FWD is also a circulating diode _D u1 _{to D un,} the switching elements X-IGBT is also the switching element _Q x1 _{to Q xn} of the lower arm, wheel diode X-FWD is also wheeling diode _{D x1} ~ D _xm is collectively shown.
As shown in FIG. 1D, during the power running operation, the current flowing through the upper-arm freewheeling diode U-FWD and the lower-arm switching element X-IGBT is larger than that of the other semiconductor elements. of as, the upper arm is connected to the m switching elements _Q u1 _{to Q um} more of n also wheeling diode _D u1 _{to D un,} the lower arm, from the m wheel diode _D x1 _{to D xm} N switching elements Q _{x1 to} Q _xn are connected.

As a result, in terms of individual semiconductor elements, elements having a current capacity of m / n can be used as individual freewheeling diodes in the upper arm, and elements having a current capacity of m / n as individual switching elements in the lower arm. Can be used. That is, as shown in FIG. 9, each semiconductor is compared with a case where a large number of semiconductor switches Q _{u1 to} Q _un and Q _{x1 to} Q _xn having the same current capacity are connected in parallel to each other, with an allowance for current capacity. It is possible to increase the current utilization factor of the element, reduce the cost, and reduce the size of the entire apparatus.
The parallel numbers m and n of the switching element and the freewheeling diode can be arbitrarily selected according to the magnitude of the phase current and the current capacity of the semiconductor element.

  This embodiment is particularly effective for a system having no regenerative function. However, as shown in FIG. 8, during regenerative operation, the current flows through the switching element U-IGBT in the upper arm and the freewheeling diode X-FWD in the lower arm. Since the current is larger than other semiconductor elements, the number of switching elements in the upper arm is set to a predetermined capacity and the number is larger than that of the freewheeling diodes. Can be reduced.

Next, FIG. 2 is a circuit configuration diagram showing a second embodiment of the present invention, FIG. 2 (a) is an overall configuration diagram, and FIG. 2 (b) is an upper and lower arm for one phase in FIG. 2 (a). semiconductor switches _Q u, the structure of _{Q x} is a diagram shown with a DC intermediate capacitor _{C d.} 2B is the same as FIG. 1B.

In this embodiment, as shown in FIG. 2 (a), the first and second switches S are provided between the positive and negative DC terminals P and N of the power conversion device 100B and the neutral point of the load M. ₁ and S ₂ are provided, and the DC switch PS is connected between the negative DC terminal N and the neutral point of the load M by closing the first switch S ₁ and opening the second switch S _2. It is, so that the DC power supply PS by closing the second switch S ₂ opens the first switch S ₁ is connected between the neutral point of the positive side DC terminals P and the load M.

3 and 4 show the operation of this embodiment, which corresponds to the powering operation mode and the regenerative operation mode, respectively. FIGS. 3 (a) and 4 (a) show the switches S ₁ and S _{2 respectively} . 3B and 4B show the waveforms of the three-phase alternating currents i _u , i _v , i _w .
3C and 4C show the configurations of the upper and lower arm semiconductor switches Q _u and Q _x for one phase. As in the first embodiment, the upper arm semiconductor switch Q _u a switching element U-IGBT of m switching elements _Q u1 _{to Q um} in FIG. 2 (b), is composed of a freewheeling diode U-FWD of n wheeling diode _D u1 _{to D un,} the lower arm The semiconductor switch Q _x includes a switching element X-IGBT composed of n switching elements Q _{x1 to} Q _xn and a _{recirculating} diode X-FWD composed of m _circulating diodes D _{x1 to} D _{xm in FIG.} It is configured.
Further, FIGS. _3D and 4D are waveform diagrams showing the U-phase current i _u and the current of each semiconductor element.

3 (a) is the power running operation, represents the opening of a second switch S ₂ closes the first switch S _1, becomes equivalent to the circuit of FIG. 1 is a circuit configuration. The operation is also the same as that of the circuit of FIG. 1, and when three-phase AC power is supplied to the load M, three-phase AC currents i _u , i _v , and i _w as shown in FIG. At this time, since the direct current i _d / 3 is superimposed on the three-phase alternating current in the negative direction, the waveforms of the three-phase alternating currents i _u , i _v , and i _w are positive and negative and asymmetric.

In addition, as shown in FIG. 3 (d), the current flowing through each semiconductor element in FIG. 3 (c) is the same as the current flowing through the upper arm freewheeling diode U-FWD and the lower arm switching element X-IGBT. More than. However, as shown in FIG. 2 (b), n switching diodes D _{u1 to} D _un more than m switching elements Q _{u1 to} Q _um are connected to the upper arm, and m _circulating currents are connected to the lower arm. Since n switching elements Q _{x1 to} Q _xn more than the diodes D _{x1 to} D _xm are connected, the current capacity of each freewheeling diode in the upper arm is m / n as in the first embodiment. In the lower arm, the current capacity of each switching element is only m / n, and the current utilization factor of each element can be improved and the cost can be reduced.

4 (a) is, during regenerative operation, and represents a second closing switch S ₂ opens the first switch S _1. At this time, three-phase alternating currents i _u , i _v and i _w as shown in FIG.
In FIG. 4B, since the direction of the current flowing through the load M is the same as that in FIG. 3B, the direct current i _d / 3 is superimposed in the negative direction on the three-phase alternating current, and the waveform thereof is also shown in FIG. Same as (b).

  Therefore, as shown in FIG. 4D, the current flowing through each semiconductor element in FIG. 4C is the same as the current flowing through the upper arm freewheeling diode U-FWD and the lower arm switching element X-IGBT. And becomes the same as in FIG. Therefore, it is possible to obtain the same effect as that during the power running operation.

Note that the first and second switches S ₁ and S ₂ in this embodiment may be either electronic switches using semiconductor elements or mechanical switches such as electromagnetic contactors. Further, both the switches S ₁ and S ₂ may be constituted by interlocking switches.
According to the present embodiment, the current utilization factor of each semiconductor element can be improved in both the power running operation mode and the regeneration mode by switching the switch.

It is the circuit block diagram and operation | movement explanatory drawing which show 1st Embodiment of this invention. It is a circuit block diagram which shows 2nd Embodiment of this invention. It is operation | movement explanatory drawing in the power running operation mode of 2nd Embodiment. It is operation | movement explanatory drawing in the regeneration operation mode of 2nd Embodiment. It is a circuit block diagram and operation | movement explanatory drawing of a prior art. It is a circuit block diagram of a prior art. It is a circuit block diagram of a prior art, and operation | movement explanatory drawing in a power running operation mode. It is a circuit block diagram of a prior art, and operation | movement explanatory drawing in a regeneration operation mode. FIG. 9 is a circuit configuration diagram for solving the problems of the prior art shown in FIGS. 7 and 8.

Explanation of symbols

100B: power converter P: positive DC terminal N: negative DC terminal U, V, W: Output terminal M: Load PS: DC power supply C _d: DC intermediate capacitor _{Q u, Q v, Q w} , Q x, _{Q y,} Q _z: semiconductor switch _{Q u1 ~Q um, Q x1 ~Q} xn: a semiconductor switching element _{D u1 ~D un, D x1 ~D} xm: wheeling diode _{S 1,} S _2: switch

Claims (3)

A power converter having a plurality of semiconductor switching elements and freewheeling diodes connected in reverse parallel to the switching elements, a load connected to an output terminal of the power converter, a neutral point of the load, and the power conversion In a power conversion system comprising a power source connected between a positive DC terminal or a negative DC terminal of the device,
A power conversion system, wherein a current capacity of the switching element or the freewheeling diode is changed according to a power running operation mode and a regenerative operation mode of the load. The power conversion system according to claim 1,
A power conversion system, wherein the current capacity of these elements is changed by changing the parallel number of the switching elements or freewheeling diodes. In the power conversion system according to claim 1 or 2,
A switch for connecting the power source between the neutral point of the load and the positive DC terminal or the negative DC terminal of the power converter according to the power running operation mode and the regenerative operation mode of the load. A power conversion system characterized by that.

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