JP2012080613A - Inverter control apparatus, and inverter control method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inverter control apparatus that can implement inverter control in a simple structure, and an inverter control method using it.SOLUTION: An inverter control apparatus 10 for controlling a phase difference φ between an inverter output voltage V and an inverter output current I to an induction heating apparatus 100 driven by an inverter power supply 20 includes a current sensor 12 for detecting the inverter output current I flowing through the induction heating apparatus 100, and a controller 15 for controlling the phase difference φ between the inverter output voltage V and the inverter output current I. The controller 15 controls the phase difference φ between the inverter output voltage V and the inverter output current I by recognizing an intermediate point tm of a period T of the inverter output voltage V, recognizing the inverter output current I at the intermediate point tm via the current sensor 12, and changing a frequency f of the inverter output voltage V according to the inverter output current I.

Description

  The present invention relates to an inverter control device that controls a phase difference between an inverter output voltage and an inverter output current for an induction heating device driven by an inverter power supply, and an inverter control method using the inverter control device.

  An induction heating device is known as a heating device that heats an object using the principle of electromagnetic induction. The induction heating apparatus has advantages such as high heating efficiency, automation and labor saving, rapid heating, easy temperature control, and improvement of working environment, and is widely used in the industrial field. The induction heating device is used, for example, in induction hardening of metal parts such as gears in an automobile factory. The induction hardening is a heat treatment technique in which electromagnetic induction is caused by high frequency electromagnetic waves and the surface of the metal part is heated for hardening.

  The induction heating device is driven by an inverter power supply because various frequencies and electric power are required depending on the shape, material, and heating conditions of the object to be heated. In the induction heating device, in order to obtain the maximum output current, it is desirable to resonate the induction heating circuit by inverter control. Here, inverter control refers to controlling the phase difference between the inverter output voltage output to the induction heating device and the inverter output current flowing through the induction heating device.

  For example, Patent Document 1 provides a phase-locked loop circuit (PLL circuit) that outputs a signal corresponding to a phase difference between an inverter output voltage and an inverter output current, and outputs an inverter output voltage and an inverter output current based on an output from the PLL circuit. The structure of the inverter control apparatus which resonates is disclosed. However, an inverter device configured using a PLL circuit represented by Patent Document 1 has many components and requires complex control.

JP-A 63-28275

  The problem to be solved is to provide an inverter control device capable of realizing inverter control with a simple configuration and an inverter control method using the same.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

  That is, according to the first aspect of the present invention, the inverter control device controls the phase difference between the inverter output voltage and the inverter output current for the induction heating device driven by the inverter power supply, and detects the inverter output current flowing through the induction heating device. And a controller for controlling a phase difference between the inverter output voltage and the inverter output current, the controller recognizes an intermediate point of the cycle of the inverter output voltage, and the current sensor Recognizing the inverter output current at an intermediate point and changing the frequency of the inverter output voltage based on the inverter output current at the intermediate point to control the phase difference between the inverter output voltage and the inverter output current Is.

  In Claim 2, It is an inverter control method using the inverter control apparatus which controls the phase difference of the output voltage and output current of an inverter with respect to the induction heating apparatus driven by an inverter power supply, Comprising: It is an intermediate | middle of the period of the said inverter output voltage Recognizing a point, recognizing the current value of the inverter output current at the intermediate point, changing the frequency of the inverter output voltage based on the current value of the inverter output current at the intermediate point, and And the phase difference between the inverter output current and the inverter output current.

  According to the inverter control device and the inverter control method using the same according to the present invention, inverter control can be realized with a simple configuration.

The block diagram which shows the induction heating apparatus which concerns on embodiment of this invention. The block diagram which similarly shows an inverter control apparatus. The graph which shows the relationship between an inverter output voltage and an inverter output current. The flowchart which shows the flow of inverter control in the case of making an inverter output voltage and an inverter output current resonate. The flowchart which shows the flow of inverter control in case an inverter output voltage and an inverter output current are made into arbitrary phase differences. (A) The block diagram which shows the inverter control apparatus of this invention (B) The block diagram which shows the conventional inverter control apparatus.

The induction heating apparatus 100 will be described with reference to FIG.
An induction heating apparatus 100 according to an embodiment of the present invention is a heating apparatus that performs induction hardening of gear parts in an automobile factory. Induction hardening is a heat treatment technique in which electromagnetic induction is caused by high-frequency electromagnetic waves, and the surface of gear parts is heated for hardening. In addition, the induction heating apparatus of this invention is not limited to the induction heating apparatus 100 which performs induction hardening.

  The induction heating device 100 includes an inverter control device 10, an inverter power supply 20, and an induction heating circuit 30. Induction heating apparatus 100 is driven by inverter power supply 20. The inverter control device 10 controls the phase difference φ between the inverter output voltage V output to the induction heating device 100 and the inverter output current I flowing through the induction heating device 100.

  The inverter power source 20 includes a three-phase AC power source 21, a rectifier 22, and an inverter circuit 23. The three-phase AC power source 21 is a commercial power source supplied to the automobile factory, and supplies a 200V or 400V three-phase AC power source. The rectifier 22 rectifies a 200V or 400V three-phase AC power supply to generate DC. The inverter circuit 23 uses a bridge circuit composed of four insulated gate bipolar transistors (IGBTs or MOSFETs) to repeatedly generate a single-phase alternating current by repeating current ON / OFF. The induction heating device of the present invention may be configured to be driven by a three-phase AC inverter, and is not limited to the induction heating device 100 driven by a single-phase AC inverter.

  The induction heating circuit 30 includes a resistor 31, a coil 32, and a capacitor 33. In the induction heating circuit 30, a resistor 31, a coil 32, and a capacitor 33 are connected in series. In the induction heating circuit 30 configured as described above, the output current of the induction heating circuit 30 is maximized by causing the inverter output voltage V and the inverter output current I to resonate.

  The inverter control device 10 includes an inverter control circuit 11 and a current sensor 12. The current sensor 12 detects the current value of the inverter output current I flowing through the induction heating device 30. The current sensor 12 is provided in the induction heating device 30 and is connected to the inverter control circuit 11.

The inverter control circuit 11 will be described with reference to FIG.
The inverter control circuit 11 includes a controller 15, an inverter drive unit 16, an A / D converter 17, and a bus 18. The controller 15 controls the phase difference φ between the inverter output voltage V output to the induction heating device 100 and the inverter output current I flowing through the induction heating device 100. The inverter drive unit 16 repeats ON / OFF of the voltage to the insulated gate bipolar transistor of the inverter circuit 23 to generate a pseudo AC waveform. The A / D converter 17 converts a current value as an analog electric signal detected by the current sensor 12 into a digital electric signal. The bus 18 is a transmission path through which each circuit including the controller 15, the inverter drive unit 16, and the A / D converter 17 exchanges data within the inverter control circuit 11.

The inverter output voltage V that is an object of inverter control will be described with reference to FIG.
FIG. 3 shows the gate output signal w (output w) for the insulated gate bipolar transistor of the inverter circuit 23, the gate output signal v (output v), the inverter output voltage V of the inverter power supply 20, The count value of the controller 15 and the inverter output current I of the induction heating circuit 30 detected by the current sensor 12 are shown. Vo represents the peak value of the inverter output voltage V, and Io represents the peak value of the inverter output current I.

  The controller 15 outputs a gate output signal w (output w) and a gate output signal v (output v) to the IGBT of the inverter circuit 23 via the inverter drive unit 16, and sends it to the induction heating circuit 13. An inverter output voltage V is supplied. At this time, the count value corresponds to the cycle T of the inverter output voltage V, and is represented as a count 0 at a point where the cycle T is 0. In FIG. 3, the inverter output current I is represented as being advanced by a phase difference φ1 with respect to the inverter output voltage V as a precondition for performing inverter control described later.

ここで、数式（Ｓ―１）は、周波数ｆを大きくした場合には、位相差φが大きくなり（インバータ出力電圧Ｖに対してインバータ出力電流Ｉが遅角する）、周波数ｆを小さくした場合には、位相差φが小さくなる（インバータ出力電圧Ｖに対してインバータ出力電流Ｉが進角する）ことを示している。 The phase difference φ between the inverter output voltage V and the inverter output current I (the phase difference of the inverter output current I with respect to the inverter output voltage V) is expressed by the following formula (S-1). R represents the resistance value of the resistor 31, L represents the inductance of the coil 32, and C represents the capacitance of the capacitor 33.

Here, in the formula (S-1), when the frequency f is increased, the phase difference φ is increased (the inverter output current I is retarded with respect to the inverter output voltage V), and the frequency f is decreased. Shows that the phase difference φ is small (the inverter output current I is advanced with respect to the inverter output voltage V).

  The flow of inverter control when the inverter output voltage V and the inverter output current I are resonated will be described with reference to FIG. As a premise for performing the inverter control, the inverter output voltage V and the inverter output current I are in the state shown in FIG. 3, that is, the inverter output current I is advanced by the phase difference φ1 with respect to the inverter output voltage V. It shall be.

  In step S110, the controller 15 recognizes the intermediate point tm in the cycle T of the inverter output voltage V. Specifically, the controller 15 recognizes the intermediate point tm from the output v to the output w (see FIG. 3). Next, in step S120, the controller 15 recognizes the current value Im as the inverter output current I of the induction heating circuit 30 at the intermediate point tm by the current sensor 12 (see FIG. 3).

  In step S130, the controller 15 determines whether or not the current value Im at the intermediate point tm is zero. When the current value Im at the intermediate point tm is 0, the controller 15 determines that the inverter output voltage V and the inverter output current I are resonating and ends the inverter control. On the other hand, when the current value Im at the intermediate point tm is not 0, the controller 15 determines that the inverter output current I is retarded or advanced with respect to the inverter output voltage V.

  In step S140, the controller 15 determines whether or not the current value Im at the intermediate point tm is greater than zero. If the controller 15 determines that the current value Im at the intermediate point tm is greater than 0, the controller 15 determines that the inverter output current I is advanced with respect to the inverter output voltage V. In step S150, the equation S-1 Thus, by increasing the frequency f of the inverter output voltage V, the phase difference φ between the inverter output voltage V and the inverter output current I is increased, and the inverter output current I is retarded with respect to the inverter output voltage V. The controller 15 repeats step S140 and step S150 until the inverter output voltage V and the inverter output current I resonate, that is, the current value Im at the intermediate point tm becomes zero.

  On the other hand, if the controller 15 determines in step S140 that the current value Im at the intermediate point tm is smaller than 0, the controller 15 determines that the inverter output current I is retarded with respect to the inverter output voltage V, and step S160. In Equation (1), by reducing the frequency f of the inverter output voltage V, the phase difference φ between the inverter output voltage V and the inverter output current I is reduced, and the inverter output current I is set to the inverter output voltage V. Advance. The controller 15 repeats Step S140 and Step S160 until the inverter output voltage V and the inverter output current I resonate, that is, the current value Im at the intermediate point tm becomes zero.

  With such a configuration, the inverter output voltage V and the inverter are changed by changing the frequency f of the inverter output voltage V so that the current value Im at the intermediate point tm of the period T of the inverter output voltage V becomes zero. The output current I can resonate.

  The flow of inverter control when the phase difference φ1 between the inverter output voltage V and the inverter output current I is controlled as an arbitrary phase difference φs will be described with reference to FIG. As a premise for performing the inverter control, the inverter output voltage V and the inverter output current I are in the state shown in FIG. 3, that is, the inverter output current I is advanced by the phase difference φ1 with respect to the inverter output voltage V. Suppose you are.

  Here, in the inverter control in which the phase difference φ1 between the inverter output voltage V and the inverter output current I is controlled as an arbitrary phase difference φs, the current sensor 12 detects the phase difference φs (hereinafter referred to as a detection timing ts). ) To detect the current value Im at the intermediate point tm described above, and control to resonate the inverter output voltage V and the inverter output current I is performed.

In step S210, the controller 15 recognizes the intermediate point tm in the cycle T of the inverter output voltage V. Specifically, the controller 15 recognizes an intermediate timing at which the output w and the output v are output as an intermediate point tm in the cycle T of the inverter output voltage V. Next, in step S220, the controller 15 shifts by the detection timing ts and recognizes the current value Im as the inverter output current I of the induction heating circuit 30 at the intermediate point tm by the current sensor 12.
Since steps S230 to S260 are the same as steps S130 to S160, the description thereof is omitted. That is, step S230 and step S260 are repeated until the current value Im at the intermediate point tm becomes zero.

  With this configuration, the inverter output voltage is set so that the current value Im at the intermediate point tm of the period T of the inverter output voltage V becomes 0 by shifting the detection timing of the current value Im by the current sensor 12 by ts. By changing the frequency f of V, the phase difference φ1 between the inverter output voltage V and the inverter output current I can be controlled as an arbitrary phase difference φs.

The effect of inverter control by the inverter control device 10 will be described with reference to FIG.
6A shows an induction heating apparatus 100 according to an embodiment of the present invention, and FIG. 6B shows a conventional induction heating apparatus 200.
In the inverter control device 210 of the conventional induction heating device 200, when the inverter output voltage V and the inverter output current I are resonated, a signal corresponding to the phase difference φ1 between the inverter output voltage V and the inverter output current I is output. A PLL circuit (not shown) is provided to resonate the inverter output voltage V and the inverter output current I with the output from the PLL circuit, and the voltage sensor 213 is required (see FIG. 6B). ).

  However, in the inverter control device 10 of the present embodiment, the inverter output voltage V and the inverter output current are based only on the current value Im of the inverter output current I of the induction heating circuit 30 at the intermediate point tm of the cycle T of the inverter output voltage V. In order to resonate with I, the voltage sensor 213 can be omitted in the inverter control device 10. That is, the inverter control device 10 can be configured with only the inverter circuit 11 and the current sensor 12.

  Further, in the inverter control device 210 of the conventional induction heating device 200, only the inverter output voltage V and the inverter output current I are made to resonate. For example, the phase difference φ between the inverter output voltage V and the inverter output current I is arbitrarily set. Could not be controlled as the phase difference φs.

  However, in the inverter control device 10 of the present embodiment, the phase difference φ between the inverter output voltage V and the inverter output current I is shifted by shifting the timing of detecting the current value Im at the intermediate point tm of the cycle T of the inverter output voltage V. Can be controlled as an arbitrary phase difference φs.

  Here, it is known that when the inverter output current I is slightly retarded with respect to the inverter output voltage V, no surge voltage is generated during ON / OFF of the current to the insulated gate bipolar transistor. The surge voltage is a large wave voltage generated instantaneously exceeding a steady state in an electric circuit or the like. Conventionally, in the inverter control device 210 of the induction heating device 200, it is necessary to provide a snubber circuit 223A in each inverter circuit 223 in order to absorb the surge voltage (see FIG. 6B).

  However, in the inverter control device 10 of the present embodiment, the phase difference φ between the inverter output voltage V and the inverter output current I can be controlled as an arbitrary phase difference φs. By controlling so that I is slightly retarded, generation of a surge voltage can be prevented. Therefore, the snubber circuit 223A that absorbs the surge voltage in the inverter power supply 20 can be omitted from each inverter circuit 223. That is, the inverter power supply 20 can be configured by the inverter circuit 223 without the snubber circuit 223A.

  Thus, according to inverter control device 10 and inverter control using the same, inverter control device 10 and inverter power supply 20 can be configured with a simple configuration, and inverter control can be realized.

ここで、数式（Ｓ―２）は、共振点で電流Ｉｏが最大となり、共振周波数から周波数をずらすことにより、電流Ｉｏを小さくコントロールできることを示している。そのため、インバータ制御装置１０は、インバータ出力電圧Ｖの周波数ｆを制御することで、誘導加熱装置１００の出力電流Ｉｏを制御することができる。 Furthermore, the relationship between the effective value Io of the inverter output current I (the output current Io of the induction heating device 100, see FIG. 3) and the effective value Vo of the inverter output voltage V is expressed by the following equation (S-2). I know.

Here, the formula (S-2) indicates that the current Io becomes maximum at the resonance point, and the current Io can be controlled to be small by shifting the frequency from the resonance frequency. Therefore, the inverter control device 10 can control the output current Io of the induction heating device 100 by controlling the frequency f of the inverter output voltage V.

DESCRIPTION OF SYMBOLS 10 Inverter control apparatus 11 Controller 12 Current sensor 20 Inverter power supply 30 Induction heating circuit 100 Induction heating apparatus V Inverter output voltage I Inverter output current φ Phase difference of inverter output voltage V and inverter output current I φ1 Inverter output voltage V and inverter output current I phase difference (before inverter control)
φs Arbitrary phase difference between inverter output voltage V and inverter output current I (arbitrary target by inverter control)
T period of inverter output voltage V tm middle point of period T of inverter output voltage V ts detection timing (timing for phase difference φs)
Im Inverter output current at the intermediate point tm of the cycle T of the inverter output voltage V f Frequency of the inverter output voltage V

Claims (2)

An inverter control device for controlling a phase difference between an inverter output voltage and an inverter output current for an induction heating device driven by an inverter power source,
A current sensor for detecting an inverter output current flowing in the induction heating device;
A controller for controlling a phase difference between the inverter output voltage and the inverter output current;
Comprising
The controller is
Recognizing the midpoint of the inverter output voltage period,
Recognizing the inverter output current at the intermediate point by the current sensor;
Based on the inverter output current at the intermediate point, change the frequency of the inverter output voltage,
Controlling a phase difference between the inverter output voltage and the inverter output current;
Inverter control device. An inverter control method using an inverter control device for controlling a phase difference between an output voltage and an output current of an inverter for an induction heating device driven by an inverter power source,
Recognizing the midpoint of the inverter output voltage period,
Recognizing the current value of the inverter output current at the intermediate point,
Based on the current value of the inverter output current at the intermediate point, change the frequency of the inverter output voltage,
Controlling a phase difference between the inverter output voltage and the inverter output current;
Inverter control method.

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