JP2023097790A - Power conversion device - Google Patents

Abstract

To provide a power conversion device for suppressing, with a simple configuration, an excessive change in a voltage applied to a smoothing capacitor.SOLUTION: A power conversion device includes a rectifier circuit, an inverter circuit, a smoothing capacitor, and a voltage holding circuit 20. The rectifier circuit converts an alternating current output from an alternating current power supply into a direct current and outputs the direct current. The inverter circuit outputs the direct current output by the rectifier circuit into the alternating current and outputs the alternating current. The smoothing capacitor smooths fluctuations contained in the direct current output from the rectifier circuit. The voltage holding circuit 20 is a circuit connected in parallel with the smoothing capacitor and includes a voltage holding capacitor 21 for absorbing power when the voltage rise occurs and outputs power when the voltage drop occurs.SELECTED DRAWING: Figure 2

Description

The present application mainly relates to a power converter that converts and outputs power output from an AC power supply.

The power conversion device of Patent Document 1 includes a converter circuit, an inverter circuit, a small-capacity first capacitor, a second capacitor, and a motor. The converter circuit rectifies the power output by the AC power supply. The inverter circuit converts the output of the converter circuit into alternating current of a predetermined voltage and frequency by switching operations of a plurality of switching elements, and outputs the alternating current to the motor. The first capacitor smoothes voltage pulsation caused by switching operations of the plurality of switching elements.

Moreover, the power conversion device of Patent Literature 1 further includes a second capacitor, a switch, and a switch control section. A second capacitor is connected in parallel with the first capacitor. A switch is connected in series with the second capacitor. The switch control section closes the switch at the timing when the voltage applied to the first capacitor becomes low. This suppresses an excessive decrease in the voltage applied to the first capacitor. On the other hand, when the voltage of the first capacitor rises, the diode conducts and power is absorbed in the second capacitor. This suppresses an excessive rise in the voltage applied to the first capacitor.

JP 2014-131446 A

The power conversion device of Patent Document 1 suppresses excessive changes in the voltage applied to the first capacitor as the smoothing capacitor with the above-described configuration. Moreover, it is desirable to suppress excessive changes in the voltage applied to the smoothing capacitor with a simple configuration different from that of Patent Document 1.

The present application has been made in view of the above circumstances, and its main purpose is to suppress excessive changes in the voltage applied to the smoothing capacitor with a simple configuration in a power converter including a smoothing capacitor. That's what it is.

The problems to be solved by the present application are as described above. Next, the means for solving the problems and the effects thereof will be described.

According to the aspect of the present application, a power converter having the following configuration is provided. That is, the power converter includes a rectifier circuit, an inverter circuit, a smoothing capacitor, and a voltage holding circuit. The rectifier circuit converts an alternating current output from an alternating current power supply into a direct current and outputs the direct current. The inverter circuit converts the direct current output by the rectifier circuit into alternating current and outputs the alternating current. The smoothing capacitor smoothes variations included in the direct current output from the rectifier circuit. The voltage holding circuit is a circuit connected in parallel to the smoothing capacitor, and includes a voltage holding capacitor that absorbs power when a voltage rise occurs and outputs power when a voltage drop occurs. include.

According to the present application, excessive changes in the voltage applied to the smoothing capacitor can be suppressed with a simple configuration.

BRIEF DESCRIPTION OF THE DRAWINGS The circuit diagram of the power converter device which concerns on one Embodiment of this application. A circuit diagram of a voltage holding circuit. 7A and 7B are graphs conceptually showing changes in the DC section voltage in the conventional example and the present embodiment when the load power changes sharply. 7 is a graph showing simulation results of changes in the DC section voltage in the conventional example and the present embodiment when the load power changes abruptly. The circuit diagram of the voltage holding circuit of a modification.

Next, embodiments of the present application will be described with reference to the drawings.

The power conversion device 1 shown in FIG. 1 converts the AC voltage and frequency output from the AC power supply 11 and outputs the converted voltage to the load 17 . Alternating current is a current or voltage that periodically changes in magnitude and direction. The power conversion device 1 can be applied to, for example, a mobile object such as a ship or an aircraft, a portable small device, or an industrial machine installed in a factory or the like. However, the application target of the power conversion device 1 is not limited to the example described above.

The AC power supply 11 outputs a three-phase AC. The AC power supply 11 may be a commercial power supply, or may be a power supply provided in a moving body or the like. The load 17 consumes power and converts it to other energy. Load 17 is, for example, a motor, lighting, or a heater. The alternating current output by the alternating current power supply 11 is not limited to three-phase alternating current, and may be single-phase alternating current.

As shown in FIG. 1 , the power conversion device 1 includes a harmonic filter 12, a rectifier circuit 13, a DC circuit 14, and an inverter circuit 15.

The alternating current output by the alternating current power supply 11 is input to the harmonic filter 12 . The harmonic filter 12 is a known filter configured with a reactor or the like. Harmonic filter 12 reduces harmonics contained in the AC output from AC power supply 11 . Harmonics are waves having frequency components that are integral multiples of the fundamental wave of alternating current. By reducing harmonics, the distortion of the AC waveform can be reduced. The harmonic filter 12 is not an essential component of the power converter 1 and can be omitted.

The alternating current output from the harmonic filter 12 is input to the rectifier circuit 13 . The rectifier circuit 13 converts alternating current into direct current. Direct current is a current or voltage that does not change direction with time. Rectifier circuit 13 includes a plurality of rectifiers. A rectifier is a device that allows current to flow in one direction only and not the other. Although the rectifiers in this embodiment are diodes, other rectifiers may be included. The rectifier circuit 13 is a three-phase bridge rectifier circuit, and each rectifier is bridge-connected. This allows alternating current to be converted to direct current. Note that when the AC power supply 11 outputs single-phase AC, a single-phase rectifier circuit is used as the rectifier circuit 13 .

The DC circuit 14 is a circuit through which the direct current output by the rectifier circuit 13 flows. A voltage holding circuit 20 and a smoothing capacitor 30 are arranged in parallel in the DC circuit 14 . Details of the voltage holding circuit 20 will be described later.

The smoothing capacitor 30 is a small-capacity capacitor. A small capacity is, for example, a capacitance of about several tens of microfarads. That is, in this specification, a capacitor with a capacitance of 1 μF or more and 100 μF or less is defined as a small-capacity capacitor. Smoothing capacitor 30 is, for example, a film capacitor or a ceramic capacitor, but may be another type of capacitor. In order to prolong the life of the power conversion device 1, it is preferable that the smoothing capacitor 30 is a capacitor of a type other than an electrolytic capacitor. However, smoothing capacitor 30 may be an electrolytic capacitor. The direct current output by the rectifier circuit 13 includes voltage fluctuations that occur when alternating current is converted to direct current. This voltage variation is called ripple. The smoothing capacitor 30 removes or reduces this ripple to smooth the voltage fluctuations.

An inverter circuit 15 is connected to the DC circuit 14 . The inverter circuit 15 converts the DC input from the DC circuit 14 into a predetermined voltage and frequency. The inverter circuit 15 includes a plurality of bridge-connected switching elements. A switching element is an element that switches between a state in which current flows and a state in which current does not flow. The inverter circuit 15 switches between opening and closing of the switching element according to a control signal output from the controller 16 to convert direct current into alternating current and output the alternating current. Although the alternating current output by the inverter circuit 15 of this embodiment is three-phase alternating current, it may be single-phase alternating current.

The controller 16 is a computer including a CPU, ROM, RAM, and the like. The CPU controls the inverter circuit 15 by reading a program stored in the ROM into the RAM and executing the program. The control signal output by the controller 16 is a signal that instructs each switching element of the inverter circuit 15 to open or close the timing.

Next, the function and configuration of the voltage holding circuit 20 will be described with reference to FIGS. 2 and 3. FIG.

The voltage holding circuit 20 is a circuit for holding the voltage supplied to the load 17 . The voltage holding circuit 20 and the smoothing capacitor 30 are arranged in parallel. The voltage fluctuation targeted by the voltage holding circuit 20 is not the ripple described above, but the voltage fluctuation of the DC circuit 14 caused by the fluctuation of the power required by the load 17 . The power required by the load 17 is hereinafter referred to as load power.

FIG. 3 shows changes in the DC section voltage of the conventional example when the load power changes. The conventional example is the power converter 1 that does not include the voltage holding circuit 20 . The DC section voltage is the voltage of the smoothing capacitor 30 of the DC circuit 14 . As shown in the load power graph of FIG. 3, the load power sharply rises at time T1. In this case, the power stored in the smoothing capacitor 30 may be insufficient because the power supply from the AC power supply 11 is not in time and the smoothing capacitor 30 has a small capacity. As a result, the DC section voltage drops significantly, and there is a possibility that the power demand of the load 17 cannot be met.

Further, as shown in the load power graph of FIG. 3, the load power sharply drops at time T2. In this case, power does not return to the AC power supply 11 due to the presence of the rectifier circuit 13 . As a result, power is concentrated in smoothing capacitor 30 . Since the smoothing capacitor 30 has a small capacity, there is a possibility that the DC voltage will rise excessively and, as a result, the smoothing capacitor 30 will be damaged.

The voltage holding circuit 20 is provided to cope with both such steep increases and decreases in load power.

As shown in FIG. 2 , the voltage holding circuit 20 includes a voltage holding capacitor 21 , a power output diode 22 and a power absorption circuit 23 .

The voltage holding capacitor 21 is arranged in parallel with the smoothing capacitor 30 . The capacitance of the voltage holding capacitor 21 is larger than that of the smoothing capacitor 30 . The voltage holding capacitor 21 holds the DC voltage when the load power suddenly changes. The voltage holding capacitor 21 is a large-capacity capacitor. A large capacity is, for example, a capacitance of about several hundred microfarads. In other words, in this specification, a capacitor with a capacity of more than 100 μF and 1000 μF or less is defined as a large-capacity capacitor. The voltage holding capacitor 21 is, for example, a film capacitor, a ceramic capacitor, or an electrolytic capacitor. Since the frequency of operation of the voltage holding capacitor 21 is lower than that of the smoothing capacitor 30, even if the voltage holding capacitor 21 is an electrolytic capacitor, it is possible to suppress the decrease in device life due to the use of an electrolytic capacitor. can.

The power output diode 22 is arranged in series with the voltage holding capacitor 21 . The power output diode 22 is a normal diode. A normal diode is a diode that is used for rectification and that does not break down at a voltage that can be generated in the power conversion device 1 . The power output diode 22 is arranged in a direction to pass the current output from the voltage holding capacitor 21 , in other words, in a direction to cut off the current input to the voltage holding capacitor 21 . As will be described later, when the load power rises sharply, the power held in the voltage holding capacitor 21 is output to the load 17 .

The power absorption circuit 23 is arranged in series with the voltage holding capacitor 21 . Also, the power output diode 22 and the power absorption circuit 23 are arranged in parallel. The power absorption circuit 23 has a function of causing the voltage holding capacitor 21 to absorb power. The power absorption circuit 23 has a power absorption diode 23a, a Zener diode 23b, and a resistor 23c. As will be described later, when the load power drops sharply, the power returned from the load is stored in the voltage holding capacitor 21 .

The power absorbing diode 23a is a normal diode. The power absorbing diode 23a is arranged in a direction to allow current absorbed by the voltage holding capacitor 21 to flow, in other words, to cut off a current output from the voltage holding capacitor 21 . In other words, the direction of the power output diode 22 and the direction of the power absorption diode 23a are opposite.

The Zener diode 23b is arranged between the power absorbing diode 23a and the resistor 23c, in other words, between the power absorbing diode 23a and the voltage holding capacitor 21. FIG. The Zener diode 23b is arranged opposite to the power absorption diode 23a. Zener diode 23b has the property of conducting current when a voltage exceeding the breakdown voltage is applied. Therefore, even if a voltage lower than the breakdown voltage is applied to the power absorption circuit 23 , no current flows from the power absorption circuit 23 to the voltage holding capacitor 21 . When a voltage exceeding the breakdown voltage is applied to the power absorption circuit 23 , current flows from the power absorption circuit 23 to the voltage holding capacitor 21 .

Therefore, it is preferable that the Zener diode 23b does not break down in the steady state and breaks down when the load power fluctuates sharply. That is, as shown in the graph surrounded by the chain line in FIG. 3, it is preferable that Vz>ΔVdc, where ΔVdc is the variation of the DC voltage in the steady state and Vz is the breakdown voltage of the Zener diode 23b. Note that the auxiliary voltage is the voltage of the voltage holding capacitor 21 . Since the fluctuation amount of the DC section voltage in the steady state includes the ripple described above, the fluctuation amount of the DC section voltage in the steady state can be calculated based on the ripple. Further, when the controller 16 controls the inverter circuit 15 to perform current noise suppression control, it is preferable to further consider the amount of variation caused by the current noise suppression control. Current noise suppression control is control for suppressing distortion when the alternating current output from the AC power supply 11 is distorted. That is, when the amount of variation due to ripple is ΔVrct and the amount of variation due to current noise suppression control is ΔVcnt, ΔVdc=ΔVrct+ΔVcnt is established. The breakdown voltage of Zener diode 23b is preferably determined in consideration of the above.

A resistor 23c is a limiting resistor for suppressing an inrush current to the voltage holding capacitor 21. FIG.

Next, the operation of voltage holding circuit 20 will be described in detail. In a steady state, voltage is applied to the voltage holding capacitor 21 , so electric power is stored in the voltage holding capacitor 21 . The charge amount is a value obtained by subtracting the breakdown voltage of the Zener diode 23b from the peak value of the charging voltage of the smoothing capacitor 30. FIG. Further, in a steady state, Vz>ΔVdc is established, so voltage fluctuations due to current noise suppression control are not suppressed by the voltage holding capacitor 21 .

Also, when the load power rises sharply as at time T1, power is first supplied from the smoothing capacitor 30 to the load 17, and as a result, the voltage of the voltage holding capacitor 21 is higher than the voltage of the smoothing capacitor 30. get higher As a result, power is supplied from the voltage holding capacitor 21 to the load 17 via the power output diode 22 . As a result, an excessive drop in the DC section voltage can be suppressed.

Also, when the load power drops sharply like time T2, the DC part voltage rises. When the DC voltage becomes higher than the sum of the auxiliary voltage and the breakdown voltage, the Zener diode 23b operates and current flows into the voltage holding capacitor 21. FIG. As a result, an excessive rise in the DC voltage can be suppressed.

Here, in the power conversion device of Patent Document 1, a switch is arranged in series with the second capacitor, and the switch is controlled to open and close depending on the situation. For example, power is supplied from the second capacitor to the motor by closing the switch at the timing when the load power of the motor rises sharply and the voltage applied to the first capacitor drops. However, in the power conversion device of Patent Document 1, the control becomes complicated because the switch needs to be controlled to open and close depending on the situation. In contrast, the voltage holding circuit 20 of the present embodiment outputs power from the voltage holding capacitor 21 and absorbs power at appropriate timing without external control. can do. Therefore, the processing of the controller 16 can be simplified compared to the configuration in which the controller 16 is used to control the operation of the voltage holding capacitor 21 .

FIG. 4 is a graph showing the results of simulation using the circuit of this embodiment with the voltage holding circuit 20 and the conventional circuit without the voltage holding circuit 20. In FIG. As shown in FIG. 4, when the load power is abruptly increased, in the present embodiment, the amount of drop in the DC section voltage is suppressed as compared with the conventional example. When the load power is abruptly lowered, the amount of increase in the DC voltage is suppressed in this embodiment as compared with the conventional example.

The circuits and elements described above are examples, and the circuits and elements may be modified to have the same or similar functionality. For example, as shown in FIG. 5, the power absorption circuit 23 can be modified. The modified power absorption circuit 23 shown in FIG. 5 drives a bipolar transistor 23d with a Zener diode 23b. That is, the bipolar transistor 23d is used as a switching element. When a voltage exceeding the breakdown voltage is applied to the Zener diode 23b, current flows through the base of the bipolar transistor 23d. As a result, the power absorbing diode 23a and the voltage holding capacitor 21 are electrically connected, and power can be stored in the voltage holding capacitor 21. FIG. The bipolar transistor 23d, which is a switching element, is driven by the Zener diode 23b. That is, the bipolar transistor 23d as a switch element is turned ON only when the Zener diode 23b is turned on. Therefore, no special drive circuitry or controls are required while using active switches.

A current, voltage, or power exceeding the rating cannot be applied to the Zener diode 23b. Therefore, when the current applied to the voltage holding circuit 20 is large, it is preferable to drive the bipolar transistor 23d with the Zener diode 23b as shown in FIG.

As described above, the power conversion device 1 of this embodiment includes the rectifier circuit 13, the inverter circuit 15, the smoothing capacitor 30, and the voltage holding circuit 20. The rectifier circuit 13 converts the alternating current output by the alternating current power supply 11 into direct current and outputs the direct current. The inverter circuit 15 converts the direct current output by the rectifier circuit 13 into alternating current and outputs the alternating current. The smoothing capacitor 30 smoothes fluctuations contained in the direct current output from the rectifier circuit 13 . The voltage holding circuit 20 is a circuit connected in parallel to the smoothing capacitor 30. The voltage holding capacitor 21 absorbs power when a voltage rise occurs and outputs power when a voltage drop occurs. including.

As a result, when the load power sharply rises and the DC voltage drops, power is output from the voltage holding capacitor 21 to the load 17 . Further, when the load power sharply drops and the DC voltage rises, power is stored in the voltage holding capacitor 21 . In other words, the power conversion device 1 can cope with both steep increases and decreases in load power.

In the power converter 1 of the present embodiment, the voltage holding circuit 20 includes a power output diode 22 connected in series with the voltage holding capacitor 21 and a power absorption circuit 23 connected in series with the voltage holding capacitor 21. ,including. A power output diode 22 and a power absorption circuit 23 are connected in parallel.

As a result, the process of outputting power from the voltage holding capacitor 21 and the process of storing power in the voltage holding capacitor 21 can be performed appropriately.

In the power conversion device 1 of the present embodiment, the power absorption circuit 23 is a voltage holding circuit 20 in which a power absorption diode 23a and a Zener diode 23b are connected in series in opposite directions.

As a result, the voltage holding circuit 20 can be operated when the DC voltage exceeds the breakdown voltage of the Zener diode 23b, in other words, when the load power fluctuates sharply. Therefore, the DC section voltage can be maintained without being controlled by the controller 16 .

In the power conversion device 1 of the present embodiment, the breakdown voltage of the Zener diode 23b is larger than the amount of voltage fluctuation in the DC steady state output from the rectifier circuit 13 .

Thereby, the voltage holding circuit 20 can be realized using the Zener diode 23b having an appropriate breakdown voltage.

In the power conversion device 1 of the present embodiment, the power absorption circuit 23 includes a resistor 23c connected in series with the Zener diode 23b and suppressing the rush current to the voltage holding capacitor 21 .

Thereby, the voltage holding capacitor can be protected.

In the power conversion device 1 of this embodiment, the capacitance of the voltage holding capacitor 21 is larger than the capacitance of the smoothing capacitor 30 .

Thereby, it is possible to make the capacitance suitable for the function of the smoothing capacitor 30 . Also, the voltage holding capacitor 21 can store and output sufficient power.

Although the preferred embodiments of the present application have been described above, the above configuration can be modified, for example, as follows.

The Zener diode 23b and the resistor 23c are not essential components and can be replaced with other elements or omitted.

The magnitude relation between the capacitances of the voltage holding capacitor 21 and the smoothing capacitor 30 is an example, and the magnitude relation may be different from that described above.

The functionality of the elements disclosed herein may be implemented by general purpose processors, special purpose processors, integrated circuits, Application Specific Integrated Circuits (ASICs), conventional circuits, and/or configured or programmed to perform the disclosed functions. Any combination of these may be implemented using circuitry or processing circuitry including. A processor is considered a processing circuit or circuit because it includes transistors and other circuits. In this disclosure, a circuit, unit, or means is hardware that performs or is programmed to perform the recited functions. The hardware may be the hardware disclosed herein, or other known hardware programmed or configured to perform the recited functions. A circuit, means or unit is a combination of hardware and software, where the hardware is a processor which is considered a type of circuit, the software being used to configure the hardware and/or the processor.

Reference Signs List 1 power conversion device 13 rectifier circuit 15 inverter circuit 20 voltage holding circuit 21 voltage holding capacitor 22 power output diode 23 power absorption circuit 23a power absorption diode 23b zener diode 23c resistor

Claims (6)

a rectifier circuit that converts the alternating current output by the alternating current power supply to direct current and outputs the result;
an inverter circuit that converts the direct current output by the rectifier circuit into alternating current and outputs the result;
a smoothing capacitor for smoothing fluctuations contained in the direct current output from the rectifier circuit;
a voltage holding circuit that is connected in parallel to the smoothing capacitor and that includes a voltage holding capacitor that absorbs power when a voltage rise occurs and outputs power when a voltage drop occurs;
A power conversion device comprising: The power converter according to claim 1,
The voltage holding circuit includes a power output diode connected in series with the voltage holding capacitor, and a power absorption circuit connected in series with the voltage holding capacitor,
A power conversion device in which the power output diode and the power absorption circuit are connected in parallel. The power converter according to claim 2,
The power conversion device, wherein the power absorption circuit is a circuit in which a power absorption diode and a Zener diode are connected in series in opposite directions. The power converter according to claim 3,
A power conversion device in which a breakdown voltage of the Zener diode is larger than a voltage fluctuation amount in a steady state of direct current output from the rectifier circuit. The power converter according to claim 3 or 4,
The power absorption circuit includes a resistor connected in series with the Zener diode to suppress rush current to the voltage holding capacitor. The power converter according to any one of claims 1 to 5,
The electric power conversion device, wherein the capacitance of the voltage holding capacitor is larger than the capacitance of the smoothing capacitor.

Images