JP2007074858A - Inverter device and refrigeration cycle device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inverter device that can reduce loss all over a wide range from a high load to a low load by employing a switching circuit formed by properly combining an IGBT and an MOSFET, and can thereby improve efficiency; and to provide a refrigeration cycle device. <P>SOLUTION: The inverter device comprises a plurality of series circuits each composed of the IGBT serving as the upstream side along the application direction of a voltage, and the MOSFET serving as the downstream side; and the switching circuit 2 in which a mutual connecting point between the IGBT and the MOSFET in the series circuit is connected to a load. By turning on/off the IGBT of at least one series circuit among the series circuits, multi-phase energization that turns on the MOSFET of at least another series circuit is sequentially switched. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an inverter device and a refrigeration cycle device that output driving power to a load, for example, a motor.

  An inverter device that outputs electric power for driving a load including an inductive component, for example, a motor, includes a switching circuit having a plurality of series circuits of two switching elements on the upstream side and the downstream side along the voltage application direction. An interconnection point of each switching element in the series circuit is connected to each phase winding of a load, for example, a brushless DC motor.

  Recently, many IGBTs and MOSFETs have been adopted as switching elements.

  In the case of a DC-DC converter using an IGBT (for example, Patent Document 1), since the voltage between both ends when the IGBT is on is constant, the loss at the time of high voltage output is small, and the driving circuit is compared with the case where a transistor is used. Becomes easy.

  In the case of an inverter device using a MOSFET (for example, Patent Document 2), there is a merit that high-frequency switching is possible because the on / off speed of the MOSFET is fast, and an output from a fan motor or the like is low because loss at low voltage output is small. Often used when driving a small motor.

  In the case of a MOSFET, there is a problem that when a large load is driven, a reverse recovery current flows through a freewheeling diode (parasitic diode) connected in reverse parallel to the MOSFET, causing a loss. In order to reduce this loss, there is a power conversion device that is provided with a reverse voltage application circuit and applies reverse voltage to the freewheeling diode at a predetermined timing to cause reverse recovery of the diode, thereby reducing the loss. (For example, Patent Document 3).

On the other hand, in recent years, low-loss power MOSFETs with further improved on-resistance characteristics of MOSFETs have been developed, and inverter devices using this element have also been developed.
Japanese Patent Laid-Open No. 2004-245452 Japanese Patent Application Laid-Open No. 7-170752 Japanese Patent Laid-Open No. 10-327585

  As described above, various elements are used as the switching elements of the inverter device. When driving a compressor mounted on a refrigeration cycle apparatus such as an air conditioner, an optimum switching element corresponding to the load characteristics is used. Must be selected. In other words, in a refrigeration cycle device such as an air conditioner, the high rotation (high output) of the compressor is limited to the start of operation, particularly when the air conditioning / refrigeration load is heavy, and when the load is stable or the spring / autumn load is light. Then, the compressor is operated for a long time at a low rotation (low output).

  If an IGBT is used as a switching element, the voltage when the IGBT is turned on is constant, so that the loss is reduced when the output current is high, but the loss reduction effect is reduced when the output current is low. . For this reason, when driving the compressor mounted in refrigeration cycle apparatuses, such as an air conditioner, the conduction | electrical_connection characteristic with a small loss reduction effect at the time of the low output is unpreferable. On the other hand, when a MOSFET is used, there is a problem that a voltage drop increases at a high current and a loss at a high load increases because of a conductive channel having a resistance characteristic.

  The present invention takes the above circumstances into consideration, and by adopting a switching circuit appropriately combining IGBT and MOSFET, loss can be reduced over a wide range from high load to low load, thereby improving efficiency. An object of the present invention is to provide an inverter device and a refrigeration cycle device that can achieve the above.

  The inverter device of the invention according to claim 1 has a plurality of series circuits of an IGBT on the upstream side and a MOSFET on the downstream side along the voltage application direction, and an interconnection point between the IGBT and the MOSFET in the series circuit is a load. A switching circuit connected to the control circuit, and a control means for sequentially switching a plurality of phases of energization for turning on and off the IGBT of at least one series circuit among the series circuits and turning on the MOSFET of at least one other series circuit; It has.

  According to the inverter device and the refrigeration cycle device of the present invention, loss can be reduced over a wide range from high load to low load, thereby improving efficiency.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
In FIG. 1, M is a brushless DC motor (load) used as a compressor motor of an air conditioner, and has a stator having three phase windings Lu, Lv, and Lw that are star-connected around a neutral point C. , And a rotor having permanent magnets. The rotor rotates due to the interaction between the magnetic field generated by the current flowing through the phase windings Lu, Lv, and Lw and the magnetic field created by the permanent magnet. The brushless DC motor M is connected with the inverter device 1 of the present invention.

  The inverter device 1 is a switching device that receives the direct current voltage Vd between the input terminals P and N to which the direct current voltage Vd is applied, and applies current to the phase windings Lu, Lv, and Lw and switches the current flow. The circuit 2 includes a control unit 10 that drives and controls the switching circuit 2.

  The switching circuit 2 has a series circuit of an IGBT (Insulated Gate Bipolar Transistor) on the upstream side and a low-loss power MOSFET on the downstream side for three phases U, V, and W along the application direction of the DC voltage Vd. Thus, an IGBT 3u is provided on the upstream side of the U phase, a MOSFET 4u is provided on the downstream side, an IGBT 3v is provided on the upstream side of the V phase, a MOSFET 4v is provided on the downstream side, an IGBT 3w is provided on the upstream side of the W phase, and a MOSFET 4w is provided on the downstream side. The free-wheeling diodes Du +, Dv +, and Dw + are connected in reverse parallel to the IGBTs 3u, 3v, and 3w, and the free-wheeling (parasitic) diodes Du−, Dv−, and Dw− are connected in reverse parallel to the MOSFETs 4u, 4v, and 4w, respectively. Yes.

  The interconnection point between the IGBT 3u and the MOSFET 4u becomes the output terminal Qu, the interconnection point between the IGBT 3v and the MOSFET 4v becomes the output terminal Qv, and the interconnection point between the IGBT 3w and the MOSFET 4w becomes the output terminal Qw. Then, the non-connection end of the phase winding Lu is connected to the output terminal Qu, the non-connection end of the phase winding Lv is connected to the output terminal Qv, and the non-connection end of the phase winding Lw is connected to the output terminal Qw. It is connected.

  The switching circuit 2 also turns on the IGBTs 3u, 3v, and 3w when the forward current flows through the free-wheeling diodes Du−, Dv−, and Dw− due to the energy stored in the phase windings Lu, Lv, and Lw. Accordingly, a reverse voltage application circuit (also referred to as a recovery assist circuit) 5u for applying a reverse voltage to the free-wheeling diodes Du-, Dv-, Dw- so that no reverse current flows through the free-wheeling diodes Du-, Dv-, Dw-. , 5v, 5w. The reverse voltage application circuits 5u, 5v, and 5w are the same as those disclosed in Japanese Patent Laid-Open No. 10-327585, and a description thereof is omitted.

The control unit 10 has the following (1) to (3) as main functions.
(1) Modulation signal generation means for generating a plurality of modulation signals having a voltage waveform fixed at a certain level as a switching pause period and having different phase angles.

  (2) A plurality of drive signals having a waveform in which the potential in the period corresponding to the switching pause period is zero level and the potential in the remaining period repeats high level and zero level by voltage comparison between each modulation signal and the triangular wave signal. Drive signal creating means for creating

  (3) In accordance with each of the drive signals, a plurality of phases of energization are sequentially performed in which at least one of the series circuits in the switching circuit 2 is turned on and off and at least one other series circuit MOSFET is turned on. Control means to switch to.

Next, the operation of the above configuration will be described.
As shown in FIG. 2, three-phase sine wave voltages Eu, Ev, Ew having a phase angle shifted by 120 degrees are prepared. The three-phase sine wave voltages Eu, Ev, Ew change in frequency in proportion to the speed of the brushless DC motor M. The three-phase sine wave voltage waveforms Eu, Ev, and Ew are shaped to correspond to 1/3 (= 2π / 3) of the period (= 2π) of the three-phase sine wave voltages Eu, Ev, and Ew. A plurality of modulation signals Eu ′, Ev ′, Ew ′ having a voltage waveform that is fixed at a negative constant level as a switching pause period and having a phase angle shifted by 120 degrees are generated.

  The modulation signals Eu ′, Ev ′, Ew ′ and the triangular wave signal Eo are compared in voltage, so that the potential in the period corresponding to the switching pause period is zero level (lower solid) and the potential in the remaining period is high. A drive signal (pulse width modulation signal; PWM signal) Vu, Vv, Vw having a lower solid energization waveform that repeats a level and a zero level is created. In response to the drive signals Vu, Vv, and Vw, multiple-phase energization in which at least one series circuit IGBT in the switching circuit 2 is turned on and off and another at least one series circuit MOSFET is turned on is sequentially switched. FIG. 3 shows operation patterns of the IGBTs 3u, 3v, 3w and the MOSFETs 4u, 4v, 4w. ○ indicates on, off, Δ indicates on, and x indicates off.

  By switching the multi-phase energization, inter-phase voltages Vuv, Vvw, Vwu corresponding to the on / off duty of the IGBT are generated between the output terminals Qu, Qv, Qw, and the inter-phase voltages Vuv, Vvw, Vwu are the phases. Applied to the windings Lu, Lv, Lw. Thereby, a sinusoidal current flows through Lu, Lv, and Lw, and the brushless DC motor M operates.

  FIG. 4 shows the relationship between the interphase voltages Vuv, Vvw, Vwu and the phase winding current. That is, under the operating conditions in which the air conditioning load is large and the IGBT on / off duty is set large (the on period is long and the off period is short), the levels and frequencies of the interphase voltages Vuv, Vvw, Vwu become high. Winding current increases. The on / off duty of the IGBT can be variably set by adjusting the level of the modulation signals Eu ′, Ev ′, Ew ′.

  As described above, the IGBTs 3u, 3v, 3w are used as the upstream side switching elements of the series circuits in the switching circuit 2, and the MOSFETs 4u, 4v, 4w are used as the downstream side switching elements of the series circuits. The IGBT is turned on and off by pulse width modulation, and multiple phase energization for turning on at least one other series circuit MOSFET is sequentially switched, so that the air conditioning load is small and the rotational speed of the brushless DC motor M may be low. At the time of load, the ON period of the MOSFET becomes longer and the ON period of the IGBT becomes shorter. Therefore, the loss of the MOSFET becomes dominant with respect to the loss, and the influence of the loss of the IGBT can be reduced. For this reason, the low-loss operation of the MOSFET can be utilized in the low-capacity operation having the highest operation time ratio such as an air conditioner.

  At the time of high load (at the time of high current), the loss of the MOSFET increases, but the on-time ratio of the upstream side IGBT also becomes longer, so that at least the upstream side switching element is IGBT than the case where all the switching elements are MOSFETs. Loss can be reduced by the amount used.

  On the other hand, when the MOSFET is used, when one of the pair of switching elements is turned on depending on the operating state, a large reverse recovery current flows through the freewheeling diode of the paired MOSFET, and the loss increases. In order to suppress this, a reverse voltage is applied to the freewheeling diode by the reverse voltage application circuits 5u, 5v, and 5w before and after the paired switching elements are turned on. As a result, a large reverse recovery current generated in the freewheeling (parasitic) diode of the MOSFET is suppressed, and loss due to the reverse recovery current can be greatly reduced. In particular, the MOSFET is used only on the downstream side, and the reverse voltage application circuits 5u, 5v, and 5w need only be provided for the downstream side MOSFETs 4u, 4v, and 4w, thereby simplifying the circuit and reducing the cost. .

  Thus, by adopting the switching circuit 2 in which the IGBT and the MOSFET are appropriately combined, the loss can be reduced over a wide range from a high load to a low load, thereby improving the efficiency of the inverter device 1.

  By the way, in the voltage comparison of the modulation signals Eu ′, Ev ′, Ew ′ and the triangular wave signal Eo shown in FIG. 2, the triangular wave signal Eo having a frequency lower than the actual frequency is adopted so that the comparison result can be easily understood. The actual triangular wave signal Eo has a higher frequency. FIG. 5 shows the relationship between the actual triangular wave signal Eo and the modulation signals Eu ′, Ev ′, Ew ′, which is enlarged in time in the 60 ° section of the phase.

  In FIG. 5, the current path of the phase winding is indicated by T1 in the first half of the 60 ° section, and the energization path based on the potential difference between the high potential modulation signal Eu ′ and the lower solid potential (zero potential) modulation signal Ev ′; An energization path is generated based on a potential difference between the modulation signal Ew ′ having a medium potential and the modulation signal Ev ′ having a lower solid potential (zero potential) indicated by T2. In the latter half of the 60 ° interval, the energization path based on the potential difference between the high potential modulation signal Eu ′ and the medium potential modulation signal Ew ′ shown in T3, and the high potential modulation signal Eu ′ and the lower solid potential (zero) shown in T4. An energization path is generated based on the potential difference between the (potential) and the modulation signal Ev ′. FIG. 6 summarizes the relationship between the on / off operation of the IGBT, the on / off duty, the phase winding current, and the current path of the inverter device 1 in these energization paths. The level of the modulation signal Ew ′ of the medium potential is a positive voltage in the first half T2, and a negative voltage in the second half T3, and the current direction and path change.

  The energization path of T1 is the path of the input terminal P, IGBT 3u, phase windings Lu and Lv, MOSFET 4v, and input terminal N as shown by the solid line in FIG. 7 when the IGBT 3u is turned on (the representative value of on and off duty is A). Current flows. When the IGBT 3u is turned off, the current based on the energy stored in the phase windings Lu and Lv passes through the MOSFET 4v from the phase windings Lu and Lv in the forward direction through the freewheeling diode Du− on the MOSFET 4u side, as indicated by the broken line in FIG. Flowing.

  In the energization path of T2, the path of the input terminal P, the IGBT 3w, the phase windings Lw and Lv, the MOSFET 4v, and the input terminal N as shown by the solid line in FIG. Current flows. When the IGBT 3w is turned off, the current based on the energy stored in the phase windings Lw and Lv passes through the MOSFET 4v from the phase windings Lw and Lv in the forward direction through the freewheeling diode Dw− on the MOSFET 4w side as indicated by the broken line in FIG. Flowing.

  In the energization path of T3, when the IGBTs 3u and 3w are on (on, the representative value of off-duty is C), the current based on the energy stored in the phase windings Lw and Lv, as shown by the solid line in FIG. Current flows from the lines Lu and Lw through the path of the freewheeling diode Dw + and IGBT 3u of the IGBT 3w. When the IGBT 3u is turned on and the IGBT 3w is turned off (on and the representative value of the off duty is AC), as shown by the broken line in FIG. 9, the current passing through the IGBT 3u and the phase windings Lu and Lw from the input terminal P is applied to the MOSFET 4w. Then, it flows to the input terminal N side. Then, when the IGBTs 3u and 3w are turned off, the current passing through the IGBT 3u and the phase windings Lu and Lw flows in the forward direction through the MOSFET 4w and the free-wheeling diode Du− on the MOSFET 4u side, as indicated by the one-dot chain line in FIG.

  In the energization path of T4, when the IGBT 3u is turned on, a current flows through the path of the input terminal P, the IGBT 3u, the phase windings Lu and Lv, the MOSFET 4v, and the input terminal N as indicated by the solid line in FIG. When the IGBT 3u is turned off, the current based on the energy stored in the phase windings Lu and Lv passes through the MOSFET 4v from the phase windings Lu and Lv in the forward direction through the freewheeling diode Du− on the MOSFET 4u side as indicated by the broken line in FIG. Flowing.

  By analyzing the current path and loss corresponding to the on / off operation of the IGBT, the analysis results are obtained for all sections of 360 ° for the currents in the four energization paths T1, T2, T3, and T4 in the 60 ° section. Can be deployed.

  That is, in the four energization paths T1, T2, T3, and T4, the loss factor that changes with the current is ignored, and it is assumed that the losses of the forward current and the reverse current of the IGBT and the MOSFET are equal. Loss is represented by IR, MOSFET loss is represented by MR, and the modulation factor is a.

  At T1, when the IGBT 3u is on, A · a · (IR + MR), and when the IGBT 3u is off, (1−A) · a · (MR + MR) = 2 · (1−A) · a · MR. Subsequently, at T2, when the IGBT 3w is on, B · a · (IR + MR), and when the IGBT 3w is off, 2 (1−B) · a · MR. In T3, when IGBT3u is on and 3w is on, 2 · C · a · IR, when IGBT3u is on and 3w is off, (AC) · a · (IR + MR), and when both IGBT3u and 3w are off, 2 · (1-A)・ A ・ MR. Finally, T4 is the same as T1, and A · a · (IR + MR) and 2 · (1−A) · a · MR.

When these are added together, the following equation is obtained.
3 ・ A ・ aIR + B ・ IR + C ・ IR + (8-3A-B-C) MR
Here, A (0 ° to 30 ° interval), B (30 ° to 60 ° interval), and C (60 ° to 90 ° interval), which are used as representative values of on and off duty, are average values. When the value at the corner is used, A is a duty at 15 ° (on time), B is a duty at 45 °, and C is a duty at 75 °. In this case, since A + B = C, if this is substituted, the following equation is obtained.
4 ・ A ・ a ・ IR + (8-4 ・ A ・ a) ・ MR
= 4.MR + 4. [A.a.IR + (1-A.a) .MR]
As can be seen from this equation, in the low output voltage region (low current region) where the modulation factor a is low, most of the current flows through the MOSFET, and the magnitude of the loss is governed by the loss of the MOSFET. Therefore, even if an IGBT is used for the upper switching element, a loss reduction effect close to that in the case where all the switching elements are MOSFETs can be obtained in this region.

  In addition, as described with reference to FIG. 4, under the operating conditions where the load is large and the on / off duty of the IGBT is set to be large, the level and frequency of the interphase voltages Vuv, Vvw, Vwu are increased and the phase winding current is increased. However, in this case, the loss ratio of the IGBT is increased, and the loss can be reduced in this region as compared with the case where all the switching elements are MOSFETs. Under actual use conditions, most of the operation time of the refrigeration cycle apparatus is a stable operation condition with a low current, and the loss reduction effect under this stable operation condition is great. On the contrary, since the MOSFET has a resistance characteristic, the loss increases as compared with the IGBT when the current increases. In such a case, since one side of the current path is the IGBT, the adverse effect can be reduced.

In other words, using a IGBT on the upper side as a switching circuit and a MOSFET on the lower side, and performing lower solid energization (two-phase modulation), loss can be reduced over a wide range from high load to low load, thereby improving efficiency. Can be planned. Also, by providing a reverse voltage application circuit, a large reverse recovery current generated in the freewheeling (parasitic) diode can be suppressed even if a MOSFET is used, and the loss can be greatly reduced. However, in the implementation stage, the constituent elements can be modified and embodied without departing from the spirit of the invention. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment.

The block diagram which shows the structure of one Embodiment of this invention. The figure which shows the waveform of each modulation signal, each drive signal, and each phase voltage in one Embodiment. The figure which shows the operation | movement pattern of each IGBT and each MOSFET in one Embodiment. The figure which shows the relationship between each phase voltage and phase winding current in one Embodiment. The figure which expands temporally and shows the relationship between the triangular wave signal and each modulation signal in one Embodiment. The figure which shows collectively the ON / OFF operation | movement of IGBT, the on / off duty, the phase winding current, and the current path in each energization pattern of one embodiment. The figure which shows the electric current path | route in FIG. 6 concretely. FIG. 7 is a diagram specifically showing another current path in FIG. 6. FIG. 7 is a diagram specifically showing another current path in FIG. 6. FIG. 7 is a diagram specifically showing still another current path in FIG. 6.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Inverter apparatus, 2 ... Switching circuit, 3u, 3v, 3w ... IGBT, 4u, 4v, 4w ... MOSFET, 5u, 5v, 5w ... Reverse voltage application circuit, Du, Dv, Dw ... Freewheeling diode, P, N ... Input terminal, Qu, Qv, Qw ... output terminal, 10 ... control unit, M ... brushless DC motor, Lu, Lv, Lw ... phase winding

Claims (3)

There are a plurality of series circuits each including an IGBT on the upstream side, a MOSFET on the downstream side, and a free-wheeling diode connected in antiparallel to each IGBT and FET along the voltage application direction, and the IGBT and MOSFET in these series circuits A switching circuit in which the interconnection point is connected to a load containing an inductive component;
Control means for sequentially switching a plurality of phases of energization for turning on / off the IGBT of at least one series circuit among the series circuits and turning on the MOSFET of at least one other series circuit;
An inverter device comprising: Each of the IGBTs is controlled so as to suppress a reverse current of each of the freewheeling diodes generated when the IGBTs are turned on when a forward current flows through the freewheeling diodes of the respective MOSFETs due to the energy stored in the load. A reverse voltage application circuit for applying a reverse voltage to each of the freewheeling diodes prior to turning on,
The inverter device according to claim 1, further comprising: A refrigeration cycle apparatus having a compressor for compressing a refrigerant, wherein the compressor is driven by the inverter apparatus according to claim 1.

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