JP2007252048A - Power controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power controller in which the rated capacity of an inverter can be reduced while improving power factor. <P>SOLUTION: In the power controller, a full-bridge circuit consisting of four self-arc-distinguishing elements S1, S4, S2 and S3 is connected in series with a single-phase snubber energy regeneration current switch 5 connected with an energy storage capacitor SC between a three-phase inverter 3 for converting DC power into AC power and a three-phase induction motor 2 which cannot control the field current. A current switch control circuit 6 for applying an on/off timing signal to each element S1-S3 and S2-S4 is provided for each phase. The control circuit 6 comprises a circuit 61 for operating a phase shift amount command corresponding to a phase shift amount obtained from the frequency command of an inverter control circuit 4, and a circuit 62 for shifting the phase such that three output phases become substantially 90° in case of long operation time frequency of the inverter 3 by receiving the phase shift amount command from the operating circuit 61 and four phase commands. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a power control device for an inverter-driven AC motor using a snubber energy regenerative current switch (magnetic energy regenerative switch: hereinafter referred to as MERS).

  Conventionally, by inserting a known MERS (see Patent Literature 1 and Non-Patent Literature 1) between a commercial power source and an induction motor, the power factor at the time of starting can be improved and the starting torque can be greatly improved. Is reported in Non-Patent Document 1.

 In the industrial field, an induction motor drive system driven by an inverter is mainly used mainly from the viewpoint of energy saving.

Induction motors have the characteristics of being robust and easy to maintain, but the excitation current must be supplied from the power supply side, so the power factor cannot be set to 1, and the inverter rating is set to the motor rating. It needs to be bigger.
Japanese Patent No. 3634982 Taku Takahisa, Takanori Isobe, Jun Naruto, Hiroaki Tsutsui, Ryuichi Shimada: "Power Factor Improvement by Current Switch that Accumulates and Regenerates Magnetic Energy", Electrical Engineering D, vol.125 No.4pp.372-377 (2005) Takuhisa Takahisa, Takanori Isobe, Ryuichi Shimada: “Improvement of starting torque of induction motor using magnetic energy regenerative bidirectional current switch”, Heisei 15 Electrical Society of Japan, 4-073 (2003) Japanese Patent Laid-Open No. 2005-57980

  In the industrial field, an induction motor drive system driven by an inverter is mainly used mainly from the viewpoint of energy saving. Induction motors have the characteristics of being robust and easy to maintain. However, since the excitation current must be supplied from the power supply side, the power factor cannot be set to 1, and the inverter rating is the motor rating. It needs to be larger than

  For this reason, particularly in a large-capacity drive system, by using a synchronous motor with a field winding, an operation with a power factor of 1 is realized and the capacity of the inverter is reduced (non-patent document). 2 and Patent Document 2).

  An object of the present invention is to provide a power control device for an inverter-driven AC motor that can improve the power factor and reduce the rated capacity of the inverter by applying MERS to the drive system of the AC motor.

The invention corresponding to claim 1
“Inverter control circuit for providing a gate control signal for turning on / off each semiconductor device of the inverter based on a frequency command, a phase command, and a voltage amplitude command, the inverter and the AC motor Are connected in series, and are composed of a plurality of self-extinguishing elements and energy storage capacitors, and each self-extinguishing element is switched in synchronization with the power cycle of the inverter to change the phase of the current flowing through the AC motor. A controllable snubber energy regenerative current switch and a timing for turning on / off each self-extinguishing element of the snubber energy regenerative current switch in accordance with the output voltage phase of the inverter, and turning on the current of the AC motor -When the current of the AC motor is turned off by turning it off at least once in a half cycle The snubber energy, the power control apparatus comprises a current switch control circuit that can be accumulated in the snubber energy recovery current switch storage capacitors. "A.

The invention corresponding to claim 4
“Consisting of a plurality of semiconductor devices, DC power can be converted into AC power by turning each semiconductor device on and off, and this converted AC power is supplied to an AC motor that cannot control the field current. An inverter control circuit for providing a gate control signal for turning on / off each semiconductor device based on the inverter, the frequency command, the phase command, and the voltage amplitude command, and the inverter A current that is connected in series between the AC motors and includes a plurality of self-extinguishing elements and energy storage capacitors, and flows through the AC motor by switching the self-extinguishing elements in synchronization with a power cycle of the inverter. Of the output frequency of the inverter and the snubber energy regenerative current switch capable of controlling the phase of the inverter Each self-extinguishing element of the snubber energy regenerative current switch is supplied with a gate signal whose phase is shifted so that the output phase of the inverter becomes approximately 90 ° when the inverter has a long operating time. A power control device comprising: a current switch control circuit that provides a control signal for turning on and off the element.

Is.

  The present invention provides a power control device that not only improves the power factor of the inverter but also stabilizes the inverter current control by connecting MERS in series between the inverter of the AC motor drive system and the AC motor. Can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, MERS5 which is an important configuration of the present invention will be described. As shown in FIG. 1, MERS 5 is inserted in series between inverter 3 that converts DC power obtained by DC power source 1 into AC power and AC motor that cannot control field current, for example, three-phase induction motor 2. An energy storage capacitor is connected to a full bridge circuit in which a half bridge composed of two self-extinguishing elements (hereinafter simply referred to as elements) S1 and S4 and a half bridge composed of two self-extinguishing elements S2 and S3 are connected. The SC is connected to each element S1-S3 and the current switch control circuit 6 is a timing signal for turning on / off the S2-S4.

  The current switch control circuit 6 has any one function described below. That is, the first of the current switch control circuit 6 gives timing for turning on / off each element of the MERS 5 in accordance with the output voltage phase of the inverter 3 and makes the current of the induction motor 2 on / off in a half cycle. By performing it at least once, the snubber energy when the current of the induction motor 2 is turned off can be stored in the storage capacitor SC of the MERS 5.

  The second of the current switch control circuit 6 is to make the reactance value of the storage capacitor SC of the MERS 5 larger than the leakage reactance value of the induction motor 2 when the frequency of the operation time of the inverter 3 is long.

  The third of the current switch control circuit 6 is such that the timing at which the MERS 5 is turned on / off is controlled in proportion to the output frequency of the inverter 3 so that the phase is 90 ° when the inverter 3 has a long operating time. To do. With this configuration, the reactance of the storage capacitor SC and the inductance corresponding to the induction motor 2 become equal, which is economical.

  The fourth of the current switch control circuit 6 uses a gate signal MERS5 whose phase is shifted so that the output phase of the inverter 3 becomes approximately 90 ° when the inverter 3 has a long operation time among the output frequencies of the inverter 3. And a control signal for turning on and off each element.

The fifth of the current switch control circuit 6 includes a phase shift amount calculation circuit 61 that calculates a phase shift amount command corresponding to the phase shift amount from the frequency command of the inverter control circuit 4, and a phase shift amount from the phase shift amount calculation circuit 61. This includes a phase shift circuit 62 that receives the command and the phase command of the inverter control circuit 4 and shifts the phase so that the output phase of the inverter 3 becomes approximately 90 ° when the frequency of the operation time of the inverter 3 is long.
A sixth current switch control circuit differs from FIG. 1 in that a phase shift amount calculation circuit (not shown) for calculating a phase shift amount command corresponding to the phase shift amount obtained from the feedback output current and output voltage of the inverter 3 is provided. The phase shift amount command from the phase shift amount calculation circuit and the phase command of the inverter control circuit 4 are input, and the phase of the inverter 3 so that the output phase of the inverter 3 becomes approximately 90 ° when the frequency of the operation time of the inverter 3 is long. Includes a phase shift circuit (not shown).

As shown in FIGS. 1 and 2, an example of the current switch control circuit 6 includes a phase shift amount command [FIG. 2 (g) corresponding to the phase shift amount from the frequency command [FIG. 2 (a)] of the inverter control circuit 4. ], A phase shift amount command from the phase shift amount calculation circuit 61 and a phase command [FIG. 2 (b)] of the inverter control circuit 4 are input, and the operation time of the inverter 3 is calculated. A phase shift circuit 62 that outputs a MERS reference phase command [FIG. 2 (h)] that shifts the phase so that the output phase of the inverter 3 becomes approximately 90 ° at a long frequency, and a current switch that takes in the MERS reference phase command. It comprises a MERS pulse generation circuit 63 that outputs a control signal and a gate driver 64 that inputs the current switch control signal and generates MERS gate pulses [FIG. 2 (i)] and [FIG. 2 (j)].
The operation principle of MERS5 described above is to cause forced series resonance by the power supply frequency between the energy storage capacitor SC and the inductance connected in series as the induction motor 2 by switching of each element S1 to S4. is there. As a result, the reactance from the inverter 3 to the induction motor 2 is reduced by using the MERS 5, and the power factor is improved.

  3 and 4 are diagrams showing the output voltage (fundamental wave component) waveform of the inverter 3 and the output current waveform of the inverter 3 when the MERS 5 is “none” and “present”, respectively. This figure is an example of the U phase. As shown in FIG. 3, when MERS5 is “none”, that is, in the case of the conventional example, the phase of the inverter output current in FIG. 3B is delayed with respect to the inverter output voltage in FIG. The power factor decreases by this amount. On the other hand, when MERS5 is “present”, that is, in the case of this embodiment, the inverter output voltage in FIG. 4A has a smaller amplitude than the inverter output voltage in FIG. The inverter output current of 4 (b) is in phase with the inverter output voltage of FIG. 4 (a), and the power factor is 1. This is because the storage capacitor SC included in the MERS 5 causes the inverter output voltage waveform in FIG. 4 (a) to be shifted by 90 ° from the inverter output voltage waveform in FIG. 3 (a) and is shown in FIG. 4 (d). The motor voltage increases in amplitude by the voltage waveform of the storage capacitor SC shown in FIG. In this case, when viewed from the motor (electric motor) 2, the voltage and current are not changed at all.

  1 includes a known inverter 3 and an inverter control circuit 4 described below. That is, the inverter 3 includes a three-phase inverter 3 including a three-phase bridge circuit in which a plurality of, for example, six semiconductor devices Su, Sv, Sw, Sx, Sy, Sz are connected in a full bridge and a capacitor C connected in parallel to the bridge circuit. The DC power can be converted into AC power by turning on and off each semiconductor device by an inverter control circuit 4 described later.

  The inverter control circuit 4 gives a gate control signal for turning on / off each semiconductor device of the inverter 3 based on the frequency command, the phase command, and the voltage amplitude command.

Specifically, the inverter control circuit 4 integrates the frequency command [FIG. 2 (a)] to obtain the phase command [FIG. 2 (b)], the phase command and the voltage amplitude command [FIG. c)] to generate a three-phase voltage command [FIG. 2 (d)], and the three-phase voltage command and carrier signal [FIG. 2 (e)] to input a gate control signal. And a gate driver 44 that receives the gate control signal and generates an inverter gate pulse [FIG. 2 (f)].
Here, the result of examination of simulation in the embodiment of the present invention will be described.

<Simulation model>
As shown in FIG. 1, the simulation model was examined by a computer simulation model in which MERS 5, 5, and 5 for three phases were inserted between the inverter 3 and the induction motor 2. The inverter 3 is a three-level PWM (pulse width modulation) inverter assuming a large capacity system, and the induction motor 2 uses a model with a rating of 6800 KW-3300 V-53 Hz. The motor power factor at the time of rating was 0.93. The MERS 5 of each phase is given a gate signal whose phase is advanced by 90 ° with respect to the current of each phase. As a result of selecting the value of the storage capacitor SU of MERS5 so as to be equal to the leakage reactance 0.22PU of the induction motor 2 model, the rated capacity of MERS5 was about 25% of the motor rating in total for the three phases.

<Stationary characteristics>
As for the steady characteristics, the power factor improvement effect of the inverter 3 by MERS5 was confirmed by simulation during rated operation. FIG. 5A is an inverter output phase voltage waveform diagram / current waveform diagram without MERS5, and FIG. 6A is an inverter output phase voltage waveform diagram / current waveform diagram with MERS5 present. The output phase voltage waveform of the inverter is a three-level PWM waveform.

  The carrier frequency is 500 Hz. When the inverter power factor is obtained from the voltage / current waveform, when there is no MERS5, the inverter power factor is the same as the motor power factor 0.93 as shown in FIG. As a result of the addition, it was confirmed that the inverter power factor was improved to 0.99 as shown in FIG. Moreover, when the current waveform diagrams of FIGS. 5 and 6 are compared, it can be seen that there is no particular deterioration in the waveform due to the addition of MERS5.

<Excessive properties>
FIG. 7 and FIG. 7 show the comparison results of the response waveforms of torque current and excitation current when the torque current command of the inverter 3 is changed stepwise from 100% → 150% → 100% during rated speed operation depending on the presence or absence of MERS. It is shown in FIG. The torque current and the excitation current are controlled by individual current control on the biaxial rotation coordinates. Non-interference control between the two-axis current control is not particularly performed. From FIG. 7, it can be seen that there is interference between the two-axis current control between the torque current and the excitation current in the absence of MERS5.

  On the other hand, it can be seen from FIG. 8 that when the MERS 5 is present, the interference between the two-axis current controls is suppressed to be small. From this, it was confirmed that MERS5 also has the effect of improving the stability of the inverter current control system when the load fluctuates. This effect is nothing other than the basic operation principle of MERS5, which is an operation itself that automatically compensates for a reactive current when an effective current flows.

  From the above, it has been confirmed that by applying MERS5 to, for example, a large-capacity induction motor drive system, there is an effect not only in improving the inverter power factor but also in stabilizing the current control of the inverter 3. In addition, when applied to a large capacity fan / pump drive, etc., it can be expected that the inverter rating for the synchronous motor drive system is disadvantageous.

<Modification>
In the above-described embodiment, a three-phase induction motor is taken as an example of the AC motor. However, the present invention is not limited to this, and any single-phase or three-phase AC motor that cannot control the field current may be used.

The schematic block diagram for demonstrating embodiment of the power control apparatus of this invention. The time chart for demonstrating operation | movement of the inverter control circuit and current switch control circuit of FIG. FIG. 2 is a waveform diagram of an output voltage and an output current of an inverter for explaining the operation effect of FIG. 1 and without MERS. FIG. 2 is a diagram for explaining the operation and effect of FIG. 1, and shows an output voltage waveform diagram and an output current waveform diagram of an inverter when there is MERS, a voltage waveform diagram of a storage capacitor of MERS, and a motor voltage waveform diagram. It is for demonstrating the effect of FIG. 1, Comprising: The output voltage waveform figure and power factor reference waveform figure of an inverter when there is no MERS. FIG. 2 is a diagram for explaining the operation and effect of FIG. 1, and is an output voltage waveform diagram and a power factor reference waveform diagram of an inverter when MERS is present. FIG. 2 is a waveform diagram of an effective component current and a reactive component current in an output current of an inverter when there is no MERS, for explaining the operation effect of FIG. 1. FIG. 2 is an effective current and reactive current waveform diagram for the output current of the inverter when the MERS is provided for explaining the operational effect of FIG. 1.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... DC power supply, 2 ... Three-phase induction motor, 3 ... Three-phase inverter, 4 ... Inverter control circuit, 41 ... Integration circuit, 42 ... Voltage command generation circuit, 43 ... PWM circuit, 44 ... Gate driver, 5 ... Single phase Snubber energy regenerative current switch (MERS), 6 ... current switch control circuit, 61 ... phase shift amount calculation circuit, 62 ... phase shift circuit, 63 ... MERS pulse generation circuit, 64 ... gate driver.

Claims (6)

It is composed of a plurality of semiconductor devices, and DC power can be converted into AC power by turning each semiconductor device on and off, and this converted AC power is supplied to an AC motor that cannot control the field current. An inverter;
An inverter control circuit for providing a gate control signal for turning on and off each semiconductor device of the inverter based on a frequency command, a phase command, and a voltage amplitude command;
The AC motor is connected in series between the inverter and the AC motor, and includes a plurality of self-extinguishing elements and an energy storage capacitor, and the self-extinguishing elements are switched in synchronization with a power cycle of the inverter. A snubber energy regenerative current switch capable of controlling the phase of the current flowing through
A timing for turning on / off each self-extinguishing element of the snubber energy regenerative current switch in accordance with the output voltage phase of the inverter is provided, and the current of the AC motor is turned on / off at least once in a half cycle. Thus, a snubber energy when the current of the AC motor is turned off can be stored in a storage capacitor of the snubber energy regenerative current switch, and a current switch control circuit,
A power control apparatus comprising:   The current switch control circuit is configured so that a reactance value of a storage capacitor of the snubber energy regenerative current switch is larger than a leakage reactance value of the AC motor when the inverter has a long operating time frequency. The power control apparatus according to claim 1.   In the current switch control circuit, the timing at which the snubber energy regenerative current switch is turned on / off is controlled in proportion to the output frequency of the inverter, and the phase is 90 ° when the inverter has a long operating time. The power control apparatus according to claim 1, wherein: It is composed of a plurality of semiconductor devices, and DC power can be converted into AC power by turning each semiconductor device on and off, and this converted AC power is supplied to an AC motor that cannot control the field current. An inverter;
An inverter control circuit for providing a gate control signal for turning on and off each semiconductor device of the inverter based on a frequency command, a phase command, and a voltage amplitude command;
The AC motor is connected in series between the inverter and the AC motor, and includes a plurality of self-extinguishing elements and an energy storage capacitor, and the self-extinguishing elements are switched in synchronization with a power cycle of the inverter. A snubber energy regenerative current switch capable of controlling the phase of the current flowing through
Each of the self-extinguishing of the snubber energy regenerative current switch is a gate signal whose phase is shifted so that the output phase of the inverter is approximately 90 ° when the inverter has a long operating time. A current switch control circuit for supplying a control signal to the element to turn on and off each self-extinguishing element;
A power control apparatus comprising:   A current switch control circuit for calculating a phase shift amount command corresponding to a phase shift amount from a frequency command of the inverter control circuit; a phase shift amount command from the phase shift amount calculation circuit; and the inverter control 2. A phase shift circuit that receives a phase command of the circuit and shifts the phase so that the output phase of the inverter becomes approximately 90 ° when the inverter has a long operating time frequency. The power control apparatus described.   The current switch control circuit includes a phase shift amount calculation circuit for calculating a phase shift amount command corresponding to a phase shift amount obtained from the feedback output current and output voltage of the inverter, and a phase shift amount command from the phase shift amount calculation circuit. And a phase shift circuit that shifts the phase so that the output phase of the inverter is approximately 90 ° when the inverter is operated at a frequency with a long operating time. The power control apparatus according to claim 1.

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