JP2015201940A - inverter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter device capable of reducing a power loss with turning-on/turning-off of switching elements.SOLUTION: The inverter device includes a switching circuit and control means. The switching circuit includes a plurality of serial circuits each formed from an unipolar wide band gap compound semiconductor device that is an upstream-side switching element, and a bipolar wide band gap compound semiconductor device that is a downstream-side switching element. Interconnection points of the upstream-side switching elements and the downstream-side switching elements in the serial circuits are connected to a load. The control means switches two-phase electrification (two-phase modulation) in which the upstream-side switching elements in two of the plurality of serial circuits are turned on intermittently and the downstream-side switching element in another serial circuit is turned on continuously, in order in the plurality of serial circuits.

Description

  The present invention relates to an inverter device that converts a DC voltage into an AC voltage.

  An inverter device that converts a DC voltage into an AC voltage includes a plurality of series circuits of two switching elements that have a relationship between an upstream side and a downstream side along the direction of current flow by application of the DC voltage, and the upstream side in these series circuits An interconnection point between the switching element and the downstream switching element is connected to each phase winding of, for example, a brushless DC motor as a load.

JP 2007-74858 A

  In the inverter device, a power loss such as a switching loss and a conduction loss caused by turning on and off the switching element occurs.

  The objective of this embodiment is to provide the inverter apparatus which can reduce the power loss accompanying ON / OFF of a switching element.

  The inverter device of claim 1 includes a switching circuit and a control means. The switching circuit includes a plurality of series circuits of a unipolar wide bandgap compound semiconductor element that is an upstream switching element and a bipolar wide bandgap compound semiconductor element that is a downstream switching element. The interconnection point between the upstream side switching element and the downstream side switching element in these series circuits is connected to the load. The control means performs two-phase energization in which the upstream switching elements of two series circuits of the plurality of series circuits are intermittently turned on and the downstream switching elements of another series circuit are continuously turned on. Switch in order in the series circuit.

The block diagram which shows the structure of one Embodiment of this invention. The figure which shows the production | generation of the PWM signal for two-phase electricity supply (two-phase modulation) of the embodiment. The figure which shows the current-loss characteristic of each switching element of the embodiment in contrast with the thing of another switching element. The block diagram which shows the structure of the modification of the embodiment.

[1] First embodiment
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 1, a rectifier circuit (also referred to as a converter) 2 is connected to a commercial AC power supply 1, and a smoothing capacitor 3 is connected to the output terminal of the rectifier circuit 2. Then, the inverter device 10 is connected to the smoothing capacitor 3.

  The inverter device 10 includes a gate drive circuit 11, a switching circuit 20, and an MCU (Micro Control Unit) 30 serving as a control unit, and converts the voltage (DC voltage) of the smoothing capacitor 3 into an AC voltage having a predetermined frequency and a predetermined level. Output. This output is supplied as drive power to, for example, a brushless DC motor M that is a load. The brushless DC motor M is composed of a stator having three phase windings Lu, Lv, and Lw that are star-connected around a neutral point C, and a rotor having a permanent magnet. The rotor rotates due to the interaction caused by attraction and repulsion between the magnetic field generated by the current flowing through the phase windings Lu, Lv, and Lw and the magnetic field generated by the permanent magnet.

  The switching circuit 20 is a U-phase series circuit of an upstream switching element 21u and a downstream switching element 22u that are in a relationship between an upstream side and a downstream side along the direction of current flow by application of a DC voltage. V-phase series circuit of the upstream switching element 21v and the downstream switching element 22v that are in the relationship between the upstream side and the downstream side along the current flow, and the upstream side and the downstream side along the current flow accompanying the application of the DC voltage The W-phase series circuit of the upstream side switching element 21w and the downstream side switching element 22w which become the relationship of these is provided. Note that free-wheeling diodes (also referred to as parasitic diodes) + Du, + Dv, + Dw are connected in reverse parallel to the upstream switching elements 21u, 21v, 21w, respectively, and free-wheeling diodes -Du, -Dv, -Dw are respectively connected in reverse parallel.

  The interconnection point between the upstream switching element 21u and the downstream switching element 22u in the U-phase series circuit is connected to the non-connected end of the phase winding Lu of the brushless DC motor, and the upstream switching element 21v and the downstream side in the V-phase series circuit The interconnection point of the switching element 22v is connected to the non-connected end of the phase winding Lv of the brushless DC motor, and the interconnection point of the upstream switching element 21w and the downstream switching element 22w in the W-phase series circuit is the phase of the brushless DC motor. It is connected to the non-connected end of the winding Lw. A resistance 23 (one shunt resistance) for winding current detection is inserted and connected in series to the negative side line of the switching circuit 20, and both ends of the resistance 23 are connected to the MCU 30. The MCU 30 detects the current flowing through the phase windings Lu, Lv, Lw of the brushless DC motor M via the resistor 23, and estimates the speed of the brushless DC motor M based on the detected current.

  The gate drive circuit 11 controls a gate signal for driving each switching element of the switching circuit 20 according to a drive control signal (PWM signal) supplied from the MCU 30 and supplied from a control power supply (not shown). It is generated using a working voltage (DC voltage) Vdd.

  In particular, the upstream side switching elements 21u, 21v, and 21w of the switching circuit 20 are unipolar wide band gap compound semiconductor elements such as MOSFETs made of silicon carbide. The downstream switching elements 22u, 22v, 22w are bipolar wide bandgap compound semiconductor elements, for example, bipolar transistors made of silicon carbide.

  In general, a material having a larger band gap than silicon or gallium arsenide is called a “wide gap semiconductor device”, and a wide gap semiconductor device that realizes characteristics with a compound of two or more elements is called a “wide gap compound semiconductor device”. Call.

  The MCU 30 has two-phase energization (so-called “so-called”) in which the upstream switching elements of two series circuits among the series circuits of the switching circuit 20 are intermittently turned on and the downstream switching elements of another series circuit are continuously turned on. In order to sequentially switch (two-phase modulation) in each series circuit, a drive control signal (PWM signal) for the switching element of each series circuit is generated.

  That is, as shown in FIG. 2, the MCU 30 generates modulation signals Eu ′, Ev ′, Ew ′, and compares the modulation signals Eu ′, Ev ′, Ew ′ with the triangular wave signal Eo to perform two-phase energization. PWM signals Vu, Vv, Vw for (two-phase modulation) are generated. By the operation of the gate drive circuit 11 in response to the PWM signals Vu, Vv, and Vw, the upstream side switching elements of the two series circuits among the series circuits of the switching circuit 20 are intermittently turned on (repetitively turned on and off). So-called lower two-phase energization in which the downstream switching elements of the remaining one series circuit are continuously turned on is sequentially switched in each series circuit. As a result, inter-phase voltages Vuv, Vvw, Vwu corresponding to the on / off duty of the upstream side switching element are generated and added to the phase windings Lu, Lv, Lw of the brushless DC motor M. As a result, a sinusoidal current flows through the phase windings Lu, Lv, Lw, and the brushless DC motor M operates.

  The modulation signals Eu ′, Ev ′, Ew ′ are obtained by waveform shaping of the three-phase sine wave voltages Eu, Ev, Ew, the phase angles differ from each other by 120 degrees, and the three-phase sine wave voltages Eu, Ev, Ew A period corresponding to 1/3 (= 2π / 3) of the period (= 2π) has a voltage waveform fixed to a negative constant level as a switching pause period. The three-phase sine wave voltages Eu, Ev, Ew change in frequency in proportion to the speed of the brushless DC motor M, and the level varies depending on the difference between the command speed input from the outside and the speed of the brushless DC motor M. Change. In the case of three-phase energization (three-phase modulation), the PWM signals Vu, Vv, V, V, Vw is generated. In response to the PWM signals Vu, Vv, and Vw, the upstream side switching elements of each series circuit are turned on and off at different phases, and the downstream side switching elements of each series circuit are turned on and off in opposite phases. Thereby, a sinusoidal current flows through the phase windings Lu, Lv, Lw of the brushless DC motor M, and the brushless DC motor M operates.

Comparing the power loss between the unipolar wide bandgap compound semiconductor device and the bipolar wide bandgap compound semiconductor device, the bipolar type in which carriers can be used for both electrons and holes has less power loss. The power loss of the switching element is roughly divided into conduction loss and switching loss. In the case of a unipolar MOSFET, “conduction loss = on resistance × current ² ”. In the case of an IGBT or a bipolar transistor, “conduction loss = saturation voltage × current”.

  Comparing the cost of the unipolar type wide bandgap compound semiconductor device and the bipolar type wide bandgap compound semiconductor device, the unipolar type such as MOSFET, which has been developed and commercialized more, has a lower cost. Moreover, in the case of two-phase energization, the energization rates of the downstream switching elements 22u, 22v, and 22w that are continuously turned on are higher than the energization rates of the upstream switching elements 21u, 21v, and 21w that are intermittently turned on.

  Therefore, a low-cost unipolar wide bandgap compound semiconductor element is used for the upstream side switching elements 21u, 21v, and 21w with the lower current ratio, and the downstream side switching elements 22u, 22v, and 22w with the higher current ratio are used. By using a bipolar wide bandgap compound semiconductor device with low power loss, power loss can be reduced as much as possible while suppressing costs.

  As a unipolar wide band gap semiconductor element, there are a MOSFET made of silicon (Si) and a SJ-MOSFET (super junction MOSFET) made of silicon. Similarly, there is a MOSFET made of silicon carbide (SiC) as a unipolar wide band gap compound semiconductor device. As a bipolar type wide band gap compound semiconductor device, there are a silicon IGBT and a silicon carbide bipolar transistor.

  The power loss of these semiconductor elements is shown in FIG. The power loss of the silicon MOSFET (Si) and the silicon SJ-MOSFET (Si) tends to be small in the low load region and greatly increased in the medium load region. The power loss of silicon IGBT (Si) increases at a constant rate in the entire load range. The power loss of the silicon carbide MOSFET (SiC) is small in the low load range and the medium load range, and increases beyond the power loss of the IGBT (Si) in the high load range. The power loss of the silicon carbide bipolar transistor (SiC) increases at a constant rate in the entire load region, but the increase is small, almost half of the power loss of the IGBT (Si). Even with the same silicon carbide, bipolar transistors have less switching and conduction losses than MOSFETs.

  In consideration of the characteristics of these semiconductor elements, MOSFETs made of silicon carbide are used as the upstream side switching elements 21u, 21v, and 21w having the lower conduction ratio, and the downstream side switching elements 22u, 22v, and 22w having the higher conduction ratio are used. A bipolar transistor made of silicon carbide with low power loss is used.

  Furthermore, silicon carbide (SiC) is superior to silicon (Si) in that the band gap is about 3 times, the dielectric breakdown electrolysis is about 10 times, the heat transfer rate is about 3 times, and it operates stably even at high temperatures. It has a physical property value. By using this silicon carbide, a switching element with high efficiency, high current density, and high switching speed can be realized. Since the switching speed is high, a smaller inductor or the like can be used, leading to a reduction in the board area.

  With the above configuration, the power loss of the inverter device 10 due to turning on and off of the switching element can be greatly reduced.

[2] Second embodiment
A second embodiment of the present invention will be described with reference to FIG.
The inverter device 10 includes a bootstrap circuit 40 in addition to the gate drive circuit 11, the switching circuit 20, and the MCU 30.

  The bootstrap circuit 40 includes diodes 41u, 41v, 41w and bootstrap capacitors 42u, 42v, 42w. When the downstream switching element 22u is on, the bootstrap circuit 40 supplies the control voltage Vdd to the diode 41u and the downstream switching element 22u. When the downstream switching element 22v is on, the bootstrap capacitor 42v is charged via the diode 41v and the downstream switching element 22v when the downstream switching element 22v is turned on. When the side switching element 22w is on, the control voltage Vdd is charged to the bootstrap capacitor 42w through the diode 41w and the downstream side switching element 22w. Then, the bootstrap circuit 40 supplies the charging voltage of the bootstrap capacitors 42u, 42v, and 42w to the gate driving circuit 11 as a power supply voltage for generating a gate signal.

The gate drive circuit 11 generates a drive gate signal for the downstream switching elements 22u, 22v, and 22w according to the drive control signal (PWM signal) supplied from the MCU 30 and using the control voltage Vdd. . Further, the gate drive circuit 11 generates a gate signal for driving the upstream side switching elements 21u, 21v, and 21w in accordance with a drive control signal (PWM signal) supplied from the MCU 30, and the bootstrap capacitors 42u, 42v, It is generated using a charging voltage of 42w.
Other configurations are the same as those of the first embodiment.

  The unipolar MOSFETs that are the upstream switching elements 21u, 21v, and 21w are voltage-driven, and the bipolar transistors that are the downstream switching elements 22u, 22v, and 22w are current-driven. A power source for driving a current-driven bipolar transistor needs to have a large capacity. On the other hand, a power source for driving a voltage-driven unipolar MOSFET is sufficient if it has a smaller capacity than a power source for driving a current-driven bipolar transistor.

  Considering this point, in the second embodiment, a driving gate signal for the downstream switching elements 22u, 22v, and 22w is generated using the control voltage Vdd, and the upstream switching elements 21u, 21v, and 21w are driven. A gate signal is generated using the charging voltage of the bootstrap circuit 40. As a result, the power supply circuit for driving the switching circuit 20 can be reduced in size and cost as a whole.

[3] Modification
In the above embodiments, each switching element of the switching circuit 20 may be modularized. By modularization, it is possible to simplify the wiring pattern and thus reduce the wiring inductance. Further, each switching element of the switching circuit 20 may be modularized together with the bootstrap circuit 40 and the gate drive circuit 11.

  In each of the above embodiments, the case where the load is a brushless DC motor has been described as an example. However, the load is not limited and can be applied to various electric devices.

  In addition, each said embodiment and modification are shown as an example, and are not intending limiting the range of invention. The novel embodiments and modifications can be implemented in various other forms, and various omissions, rewrites, modifications, portions of the embodiments and modifications can be made without departing from the spirit of the invention. Combinations can be made. In these embodiments and modifications, the scope of the invention is included in the gist, and is included in the invention described in the claims and the equivalents thereof.

  DESCRIPTION OF SYMBOLS 1 ... Commercial AC power source, 2 ... Rectifier circuit, 3 ... Smoothing capacitor, 10 ... Inverter device, 11 ... Gate drive circuit, 20 ... Switching circuit, 21u, 21v, 21w ... Upstream switching element, 22u, 22v, 22w ... Downstream Side switching element, M ... brushless DC motor (load), 30 ... MCU, 40 ... bootstrap circuit, 41u, 41v, 41w ... diode, 42u, 42v, 42w ... bootstrap capacitor

Claims (4)

It has a plurality of series circuits of a unipolar wide band gap compound semiconductor element that is an upstream switching element and a bipolar wide band gap compound semiconductor element that is a downstream switching element, and the upstream switching element and the downstream in these series circuits A switching circuit in which the interconnection point of the side switching elements is connected to the load;
Two-phase energization in which the upstream switching elements of two series circuits are intermittently turned on and the downstream switching elements of another series circuit is continuously turned on in the plurality of series circuits is sequentially performed in the plurality of series circuits. Control means for switching;
An inverter device comprising: The unipolar wide bandgap compound semiconductor device is a silicon carbide MOSFET,
The inverter device according to claim 1, wherein the bipolar wide band gap compound semiconductor element is a bipolar transistor made of silicon carbide. A bootstrap circuit including a capacitor charged with a control voltage by turning on the downstream switching element;
A gate drive circuit for generating a gate signal for driving the downstream switching element using the control voltage, and generating a gate signal for driving the upstream switching element using the voltage of the capacitor;
The inverter device according to claim 1, further comprising:   4. The inverter device according to claim 3, wherein each switching element of the switching circuit is modularized, or each switching element of the switching circuit is modularized together with the bootstrap circuit and the gate drive circuit. .

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