JP7590909B2 - AC to DC converter - Google Patents

Description

The present invention relates to a technology for converting AC voltage to DC voltage and a technology for converting AC voltage to AC voltage.

The configuration shown in FIG. 1 is known as an AC/DC converter that converts AC voltage to DC voltage. This AC/DC converter includes a converter 11 that rectifies the input three-phase AC voltage to a DC voltage, a smoothing capacitor 12 that smoothes the DC voltage, a step-down circuit 30 that steps down the DC voltage, and a step-up circuit 40 that steps up the DC voltage. The converter 11 includes diodes 111-116 that rectify the three-phase AC voltage in a fixed direction (from bottom to top in the figure). The step-down circuit 30 includes a transistor 31 that performs switching operations for stepping down, a diode 32, and an inductor 33. The step-up circuit 40 includes a transistor 41 that performs switching operations for stepping up, and a diode 42. The inductor 33 is shared by the step-down circuit 30 and the step-up circuit 40.

Japanese Patent Application Publication No. 9-149643

The reason why both the step-down circuit 30 and the step-up circuit 40 are provided in the AC-DC converter in FIG. 1 is that the DC voltage after rectification in the converter 11 may be higher or lower than the target voltage. The table on the right of FIG. 1 shows the AC voltage input to the converter 11 and the DC voltage after rectification in the converter 11 (√2 times the input AC voltage), and the DC voltage after rectification may be higher or lower than the target voltage of 320V. If the DC voltage after rectification is higher than the target voltage of 320V, it is stepped down to the target voltage by the step-down circuit 30, and if the DC voltage after rectification is lower than the target voltage of 320V, it is stepped up to the target voltage by the step-up circuit 40. In this way, when the DC voltage after rectification in the converter 11 can be higher or lower than the target voltage, both the step-down circuit 30 and the step-up circuit 40 are required, which leads to a complex configuration and increased costs.

The present invention was made in consideration of these circumstances, and its purpose is to provide an AC/DC converter and an AC converter that have a simple configuration.

In order to solve the above problems, an AC-DC converter according to one embodiment of the present invention includes a rectifier that rectifies an input AC voltage to a DC voltage, a smoothing capacitor that smoothes the rectified DC voltage, a boost capacitor connected in series with the smoothing capacitor, and a mode switching unit that can switch between a boost mode in which a charging path is formed to charge the boost capacitor with the input AC voltage and the DC voltage output by the rectifier is increased by the charged boost capacitor, and a normal mode in which no charging path is formed.

According to this embodiment, the DC voltage output by the rectifier can be increased by the boost mode using the boost capacitor, eliminating the need to provide a boost circuit downstream of the rectifier.

Another aspect of the present invention is an AC conversion device. This device includes a rectifier unit that rectifies an input AC voltage to a DC voltage, a smoothing capacitor that smoothes the rectified DC voltage, a boost capacitor connected in series with the smoothing capacitor, a charging path that charges the boost capacitor with the input AC voltage, and a mode switching unit that can switch between a boost mode in which the DC voltage output by the rectifier unit is increased by the charged boost capacitor and a normal mode in which a charging path is not formed, and a DC-AC conversion unit that converts the DC voltage output by the rectifier unit into an AC voltage.

In addition, any combination of the above components, and any transformation of the present invention into a method, device, system, recording medium, computer program, etc., are also valid aspects of the present invention.

The present invention provides an AC/DC converter and an AC converter with a simple configuration.

1 shows a conventional AC to DC converter. 1 shows a schematic configuration of an inverter device. An example in which this embodiment is applied to the example of FIG. 1 will be described.

Below, the embodiments for implementing the present invention will be described in detail with reference to the drawings. In the description and drawings, the same or equivalent components, members, and processes are given the same reference numerals, and duplicated descriptions are omitted as appropriate. The scale and shape of each part shown in the drawings are set for convenience in order to facilitate explanation, and should not be interpreted as being limiting unless otherwise specified. The embodiments are illustrative and do not limit the scope of the present invention in any way. All features and combinations thereof described in the embodiments are not necessarily essential to the invention.

Figure 2 shows a schematic configuration of an inverter device 10 as an embodiment of the AC conversion device of the present invention. The inverter device 10 includes a converter 11 as a rectifier that rectifies a multi-phase AC voltage having different phases input from an AC power source and converts it into a DC voltage, a smoothing capacitor 121 that smoothes the DC voltage rectified by the converter 11 to shape the waveform, a step-down circuit 30 as a step-down unit that steps down the DC voltage rectified by the converter 11, a smoothing capacitor 130 that smoothes the DC voltage stepped down by the step-down circuit 30 to shape the waveform, and an inverter 13 as a DC-AC conversion unit that converts the DC voltage stepped down by the step-down circuit 30 into an AC voltage.

Converter 11 is equipped with diodes 111 to 116 that rectify the three-phase (U, V, W) AC voltage input from the AC power source in a fixed direction (from bottom to top in the figure). Diode 111 passes current when the U-phase AC voltage is positive, diode 112 passes current when the U-phase AC voltage is negative, diode 113 passes current when the V-phase AC voltage is positive, diode 114 passes current when the V-phase AC voltage is negative, diode 115 passes current when the W-phase AC voltage is positive, and diode 116 passes current when the W-phase AC voltage is negative. These diodes 111 to 116 connected in a bridge form cause a pulsating current with a fixed direction and fluctuating magnitude to appear between high-potential output terminal 117 and low-potential output terminal 118 of converter 11. The smoothing capacitor 121 and the boost capacitor 122 (described later) smooth out the pulsating current obtained by the converter 11 to generate a DC voltage with a regular waveform.

The step-down circuit 30 includes a transistor 31 that is connected to the high potential output terminal 117 of the converter 11 and performs a switching operation for stepping down, a diode 32 that is connected between the output stage of the transistor 31 and the low potential output terminal 118 of the converter 11 and passes a current from the low potential side to the high potential side, and an inductor 33 that is connected to the output stage of the transistor 31 and outputs a stepped-down DC voltage. When the transistor 31 is on, the high potential _VDC from the high potential output terminal 117 of the converter 11 is applied to the inductor 33, and when the transistor 31 is off, the low potential _Vss from the low potential output terminal 118 of the converter 11 is applied to the inductor 33 via the diode 32.

As a result, the inductor 33 outputs a _DC potential _Vout between the high potential VDC and the low potential _Vss according to the on/off ratio of the transistor 31. That is, if the on time of the transistor 31 in the operation cycle T of the step-down circuit 30 is T _ON and the off time is T _OFF (T=T _ON +T _OFF ), then _Vout ≈ (T _{ON VDC} +T _{OFF Vss} )/(T _ON +T _OFF ). With this step-down circuit 30, the high potential _VDC output by the converter 11 can be stepped down to any DC potential _Vout that is equal to or lower than the high potential _VDC and equal to or higher than the low potential _Vss . As an extreme case, when the transistor 31 is always on during the operation cycle T of the step-down circuit 30 (T=T _ON ), V _out ≈ V _DC and the high potential V _DC does not drop, whereas when the transistor 31 is always off during the operation cycle T of the step-down circuit 30 (T=T _OFF ), V _out ≈ V _ss and the high potential V _DC drops to the minimum potential V _ss .

In the above configuration, the converter 11, the smoothing capacitor 121 (and the boost capacitor 122), and the step-down circuit 30 (and the smoothing capacitor 130) constitute an AC-DC converter of the present invention that converts an AC voltage input from an AC power source into a DC voltage. The DC voltage input between the high potential input terminal 131 and the low potential input terminal 132 of the inverter 13 through such an AC-DC converter is represented as _Vin . If the potential of the high potential input line to which the high potential input terminal 131 is connected is _Vdd , and the potential of the low potential input line to which the low potential input terminal 132 is connected is _Vss , then _Vin = _Vdd - _Vss . Here, the potential _Vdd of the high potential input line is equal to the DC potential Vout _output by the inductor 33. Hereinafter, unless otherwise specified, _Vin is assumed to be constant (for example, a target voltage of 320V, which will be described later).

The inverter 13 converts a DC voltage _Vin input between a high potential input terminal 131 and a low potential input terminal 132 into a three-phase AC voltage. Specifically, a U-phase inverter 13U that generates a U-phase AC voltage based on the DC voltage _Vin , a V-phase inverter 13V that generates a V-phase AC voltage based on the DC _voltage Vin, and a W-phase inverter 13W that generates a W-phase AC voltage based on the DC voltage _Vin are provided in parallel. Since the inverters 13U, 13V, and 13W of each phase have a common configuration, they will be collectively referred to as inverter 13 below as appropriate.

The inverter 13 includes a high potential input terminal 131 to which a high DC power supply potential _Vdd is input, a low potential input terminal 132 to which a low DC power supply potential _Vss is input, and an output terminal 133 that is provided between the high potential input terminal 131 and the low potential input terminal 132 and outputs an AC voltage that fluctuates between _Vdd and _Vss . A high potential transistor 134H is connected between the high potential input terminal 131 and the output terminal 133, and a low potential transistor 134L is connected between the low potential input terminal 132 and the output terminal 133. The high potential transistor 134H has its conduction state switched in response to a control signal from a high potential driver 135H connected to its control electrode. The low potential transistor 134L has its conduction state switched in response to a control signal from a low potential driver 135L connected to its control electrode.

Specifically, the driver pair 135 consisting of the high potential driver 135H and the low potential driver 135L converts the DC voltage into an AC voltage by performing switching control to complementarily switch the conductive state of the transistor pair 134 consisting of the high potential transistor 134H and the low potential transistor 134L. Here, "complementarily switch" means controlling the on and off states of the transistors 134H and 134L to be opposite to each other. That is, when the transistor 134H is on, the transistor 134L is turned off, and when the transistor 134L is on, the transistor 134H is turned off. As a result, when the high potential transistor 134H is on, a high potential _Vdd appears at the output terminal 133, and when the low potential transistor 134L is on, a low potential _Vss appears at the output terminal 133. By periodically repeating such switching control, the high potential _Vdd and the low potential _Vss appear alternately at the output terminal 133, generating an AC voltage.

The three-phase AC voltage generated by the inverter 13 is used to drive the motor 20, for example. The motor 20 is a three-phase brushless motor having three-phase coils 20U, 20V, and 20W, i.e., U-phase, V-phase, and W-phase. The U-phase coil 20U is applied with a U-phase voltage from the U-phase inverter 13U, and a U-phase current flows through it. The V-phase coil 20V is applied with a V-phase voltage from the V-phase inverter 13V, and a V-phase current flows through it. The W-phase coil 20W is applied with a W-phase voltage from the W-phase inverter 13W, and a W-phase current flows through it. The inverters 13U, 13V, and 13W of each phase apply AC voltages of different phases to the coils 20U, 20V, and 20W of each phase based on the rotational position of the rotor detected by the hall elements H1, H2, and H3 of the motor 20, thereby generating a rotating magnetic field. The desired rotational power is obtained from the rotor that rotates due to this rotating magnetic field. The motor 20 may be another type of motor driven by an AC voltage. Furthermore, the number of phases of the motor 20 is not limited to three and may be any natural number. Similarly, the number of phases of the AC voltage input to the converter 11 is not limited to three and may be any natural number.

Next, a description will be given of the boost capacitor 122 for increasing the _DC voltage VDC output by the converter 11. The boost capacitor 122 has the same capacity as the smoothing capacitor 121, and is connected in series with the smoothing capacitor 121 between the high potential output terminal 117 and the low potential output terminal 118 of the converter 11. The smoothing capacitor 121 is disposed on the high potential side, and the boost capacitor 122 is disposed on the low potential side.

A switch 60 that can be switched between a first contact 61 and a second contact 62 is provided between a connection 123 between the smoothing capacitor 121 and the boost capacitor 122 and an input terminal for an AC voltage of at least one arbitrary phase (W phase in the illustrated example) of the three-phase AC voltage input from the AC power source to the converter 11. When the switch 60 is connected to the first contact 61, the converter 11 operates in a normal mode, and when the switch 60 is connected to the second contact 62, the converter 11 operates in a boost mode, which will be described later.

In the boost mode, a charging path 124 is formed to apply the W-phase AC voltage to a connection 123 between the smoothing capacitor 121 and the boost capacitor 122. When the W-phase AC voltage is positive, the boost capacitor 122 is charged by this charging path 124, and the DC voltage (V _DC -V _ss ) output by the converter 11 increases due to the charged boost capacitor 122.

When the W-phase AC voltage is positive, the boost capacitor 122 is charged to the peak voltage Vp by the WU interphase voltage or WV interphase voltage applied between the connection part 123, which has a positive potential due to the W-phase AC voltage, and the low-potential output terminal 118, which has a negative potential due to the U-phase or V-phase AC voltage. Also, when the W-phase AC voltage is negative, the smoothing capacitor 121 is charged to the peak _{voltage Vp} by the UW interphase voltage or VW interphase voltage applied between the high-potential output terminal 117, which has a positive potential due to the U-phase or V-phase AC voltage, and the connection part 123, which has a negative potential due to the W-phase AC voltage. As a result, _2Vp, which is the sum of the voltages of the smoothing capacitor 121 and the boost capacitor 122, appears between the output terminals 117, 118 of the converter 11.

In contrast to the above-described boost mode, in normal mode in which switch 60 is connected to first contact 61, smoothing capacitor 121 and boost capacitor 122 function as a single capacitor and are charged overall to peak voltage _Vp by the UVW interphase voltages. As a result, peak voltage _Vp appears between output terminals 117, 118 of converter 11. In this way, the DC voltage ( _2Vp ) output by converter 11 in the boost mode is a constant multiple (2 times) of the DC voltage ( _Vp ) output by converter 11 in the normal mode.

The example shown in the figure combines a smoothing capacitor 121 with one boost capacitor 122 to obtain an output voltage twice the normal level, but by combining two or more boost capacitors, an output voltage three or more times the normal level can be obtained. Such circuits are called voltage multipliers or voltage multiplier circuits, and well-known examples include the Cockcroft-Walton circuit, which is made up of multiple stages of capacitors and diodes.

A mode switching unit 50 is provided to switch between the normal mode and the boost mode as described above. The mode switching unit 50 switches to the boost mode when the DC voltage output by the converter 11 in the normal mode is lower than a predetermined target voltage. Specifically, the mode switching unit 50 monitors the AC voltage of at least one phase of the three-phase AC voltage input to the converter 11 from the AC power source, and switches between the normal mode and the boost mode by switching the switch 60 between the first contact 61 and the second contact 62 according to the comparison result between the output voltage of the converter 11 calculated from the monitor and the target voltage.

As explained with respect to the table in FIG. 1, the output voltage of converter 11 indicated as "after rectification" can be calculated as √2 times the input voltage of converter 11 indicated as "AC input". Therefore, in the illustrated example, if the input voltage of converter 11 is 180V-220V, it can be seen that the output voltage of converter 11 in normal mode will be lower than the target voltage of 320V. Therefore, the mode switching unit 50 switches to the boost mode so that the output voltage of converter 11 is higher than the target voltage of 320V. On the other hand, if the input voltage of converter 11 is 230V-265V, it can be seen that the output voltage of converter 11 in normal mode will be higher than the target voltage of 320V. In this case, the mode switching unit 50 operates converter 11 in normal mode.

Figure 3 shows an example in which this embodiment is applied to the example in Figure 1. As described above, when the input voltage of converter 11 is 180V-220V, the mode switching unit 50 operates converter 11 in boost mode (voltage doubler rectification), resulting in the output voltage (after rectification) of converter 11 being higher than the target voltage of 320V. On the other hand, when the input voltage of converter 11 is 230V-265V, converter 11 operates in normal mode (general rectification), and a DC voltage higher than the target voltage of 320V is output even without switching to boost mode.

In this way, by appropriately using the boost mode, the output voltage of the converter 11 becomes higher than the target voltage, regardless of the input voltage of the converter 11. The step-down circuit 30 downstream of the converter 11 can generate the target voltage (320V) by stepping down the output voltage of the converter 11. Since there is no need to provide a boost circuit 40 downstream of the converter 11 as in Figure 1, the configuration can be simplified and costs can be reduced.

The present invention has been described above based on the embodiments. The embodiments are merely examples, and it will be understood by those skilled in the art that various modifications are possible in the combination of each component and each processing process, and that such modifications are also within the scope of the present invention.

The functional configuration of each device described in the embodiments can be realized by hardware resources or software resources, or by the cooperation of hardware and software resources. Processors, ROM, RAM, and other LSIs can be used as hardware resources. Programs such as operating systems and applications can be used as software resources.

10 inverter device, 11 converter, 13 inverter, 20 motor, 30 step-down circuit, 50 mode switching unit, 60 switch, 121 smoothing capacitor, 122 boost capacitor, 123 connection portion, 124 charging path.

Claims (3)

A rectification unit that rectifies an input AC voltage into a DC voltage;
a smoothing capacitor for smoothing the rectified DC voltage;
a boost capacitor connected in series with the smoothing capacitor;
a mode switching unit capable of switching between a boost mode in which a charging path for charging the boost capacitor is formed by an input AC voltage and the DC voltage output from the rectifier is increased by the charged boost capacitor, and a normal mode in which the charging path is not formed;
a step-down unit that steps down the DC voltage rectified by the rectification unit;
Equipped with
The step-down unit steps down the DC voltage rectified by the rectification unit to a predetermined target voltage,
the mode switching unit switches to the voltage boosting mode when the DC voltage output by the rectification unit in the normal mode is lower than the target voltage.
AC to DC converter. A multi-phase AC voltage having mutually different phases is input to the rectification unit,
the charging path is a path for applying an AC voltage of at least one phase among the multi-phase AC voltages to a connection portion of the smoothing capacitor and the boosting capacitor;
2. The AC/DC converter according to claim 1. The AC-DC converter according to claim 1 or 2, wherein the DC voltage output by the rectifier in the boost mode is a constant multiple of the DC voltage output by the rectifier in the normal mode.

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