JP2011130525A - Electric motor drive system - Google Patents

Abstract

[PROBLEMS] To drive a plurality of AC motors by a single drive device (power converter), and to use a stator having the same winding method to suppress an increase in the cost of the entire system and An electric motor drive system that suppresses occurrence and reduces copper loss is provided.
In a motor drive system in which n (n is an integer of 2 or more) AC motors are driven by a single inverter 400, for example, a terminal voltage less than or equal to 1/2 of the voltage that can be output by the inverter 400 is applied. Two possible AC motors 101 and 201 are connected in tandem, the windings of these AC motors 101 and 201 are connected in series for each phase, and the phases of the induced voltages are matched.
[Selection] Figure 1

Description

  The present invention relates to a motor drive system that drives a plurality of AC motors coupled in series (tandem coupling) with a power converter such as an inverter.

It is known that there are manufacturing restrictions on the dimensions, ratings, etc. of the motor, and when the required output cannot be obtained with one motor, the required output is obtained by tandemly coupling a plurality of motors. .
FIG. 8 is a schematic configuration diagram when two AC motors are connected in tandem. For example, 101 ′ and 201 ′ are three-phase permanent magnet motors, and 102 and 202 are motors 101 ′ and 201 ′. A rotating shaft 300 indicates a load (coupling). In FIG. 8, for example, if the output of one motor is 100 [kW], a total of 200 [kW] can be obtained.

  Here, Patent Document 1 discloses a rotating electrical machine in which a plurality of sets of two rotating armatures fixed to one shaft are coupled in tandem. However, this prior art is an invention related exclusively to the structure of a rotating electrical machine and does not describe any driving method thereof, and it is presumed that normally the same number of driving devices as the rotating armature are required.

  In the system as shown in FIG. 8, in order to rotate the load 300 in one direction, the rotation directions of the electric motor 101 'and the electric motor 201' must be reversed. At that time, if each motor 101 ′, 201 ′ is driven by an individual drive device, the rotation direction can be determined by each drive device, so the phase sequence of the windings of the motor 101 ′, 201 ′ does not matter. . That is, it is possible to use an electric motor having a stator with the same winding method. However, on the other hand, as many drive devices as the number of electric motors (stators) are required, there is a concern that costs increase.

On the other hand, when two electric motors are driven by one drive device, the phase sequence of the windings of each electric motor must be reversed.
For example, FIG. 9 is an example (concentrated winding) of the windings of the two electric motors 101 ′ and 201 ′ shown in FIG. 8, and the electric motors 101 ′ and 201 ′ are arranged in the axial direction from the load 300 side in FIG. It shows the state as seen. As is apparent from FIG. 9, in one motor 101 ′, windings U ₁ , V ₁ , W ₁ , U ₂ , V ₂ , W ₂ of the three phases are wound counterclockwise, and the other motor 201 In ', the windings U ₁ , V ₁ , W ₁ , U ₂ , V ₂ , W ₂ are wound clockwise. That is, it is necessary to manufacture two stators with different winding methods.
In FIG. 9, 103 and 203 denote rotor cores, 104 and 204 denote permanent magnets, and 105 and 205 denote stator cores.

  Further, when two electric motors are driven by one driving device, as shown in FIG. 10, the stator windings of the two electric motors 101 ′ and 201 ′ with respect to the three-phase inverter 400 as the driving device. A method of connecting lines in parallel is conceivable. However, in the case where the motors 101 ′ and 201 ′ are permanent magnet type motors, there is a problem in that a cross current occurs between the motors 101 ′ and 201 ′ if the phases of the induced voltages of the motors 101 ′ and 201 ′ do not match. .

Japanese Patent Laid-Open No. 4-190665 (FIGS. 1 to 4 etc.)

As described above, when each of the two electric motors is driven by an individual driving device, the cost increases.
Further, when two electric motors are driven by one driving device, it is necessary to manufacture two stators with different winding methods. Furthermore, when two permanent magnet type motors are connected in parallel and driven by a single drive unit, a cross current occurs if the phase of the induced voltage does not match in each motor, resulting in an increase in copper loss. There was a problem.

  Therefore, the problem to be solved by the present invention is that a plurality of AC motors can be driven by a single drive device (power converter), and a stator having the same winding method can be used, which increases the cost of the entire system. It is providing the electric motor drive system which suppressed copper loss by suppressing generation | occurrence | production of a cross current.

In order to solve the above problem, an electric motor drive system according to claim 1 is an electric motor drive system in which n (n is an integer of 2 or more) AC motors are driven by a single power converter.
Tandem coupling of n AC motors capable of applying a terminal voltage of 1 / n or less of the voltage that can be output from the power converter, and connecting the windings of these AC motors in series for each phase, The phase of the induced voltage of all AC motors is matched.

  The electric motor drive system according to claim 2 is the electric motor drive system according to claim 1, wherein the rotating shafts of two AC electric motors having the same winding method of the stator winding are connected to each other through a load. The phase sequence of the windings of each motor viewed from the load is opposite to each other.

  According to the present invention, a plurality of AC motors can be driven by a single power converter such as an inverter, and a stator having the same winding method can be used, thereby reducing the cost of the entire system. it can. Further, by connecting the windings of each motor in series for each phase, it is possible to suppress the occurrence of cross current.

1 is an overall configuration diagram of an electric motor drive system according to a first embodiment of the present invention. FIG. 2 is a conceptual connection diagram of stator windings of two electric motors in FIG. 1. It is a circuit diagram of the principal part of the inverter in FIG. It is an output voltage command of an inverter at the time of sine wave modulation, and a waveform diagram of a carrier. It is a wave form diagram of the output voltage command and line voltage command of an inverter at the time of 2 arm modulation. It is a wave form diagram of the output voltage command and line voltage command of an inverter at the time of trapezoidal wave modulation. It is a whole block diagram of the electric motor drive system which concerns on 2nd Embodiment of this invention. It is a schematic block diagram at the time of combining two electric motors in tandem. It is explanatory drawing of the coil | winding of each electric motor of FIG. It is a schematic block diagram in the case of connecting and driving two electric motors in parallel.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1 and 2 show a first embodiment of the present invention. FIG. 1 is an overall configuration diagram of an electric motor drive system, and FIG. 2 is a conceptual connection diagram of stator windings of two electric motors. .

In FIG. 1, reference numerals 101 and 102 denote tandem-coupled three-phase permanent magnet type motors, and these rotary shafts 102 and 202 are coaxially coupled via a load (coupling) 300.
Reference numeral 400 denotes a power converter (three-phase inverter) as an electric motor drive device. The other end of the cable 501 whose one end is connected to its output terminals U, V, W (see FIG. 3) is connected to the first electric motor 101. It is connected to the winding input terminal 111. Further, the winding output terminal 112 of the electric motor 101 is connected to the winding input terminal 211 of the second electric motor 201 via the cable 502.

Next, in FIG. 2, U1, V1, and W1 are the respective phase windings of the stator of the first motor 101, and the terminal with the suffix in is connected to the winding input terminal 111, and the suffix is out. The terminals marked with are connected to the winding output terminal 112. U 2, V 2, and W 2 are the phase windings of the stator of the second motor 102, and the terminal with the suffix “in” is connected to the winding input terminal 211, and further via the cable 502 The first motor 101 is connected to terminals U1 _out , V1 _out , and W1 _out of the phase windings U1, V1, and W1, respectively.
That is, the windings U1, V1, W1, U2, V2, and W2 of the electric motors 101 and 201 are connected in series for each phase.

Next, the voltage that can be output from the three-phase inverter 400 in this embodiment will be described.
FIG. 3 is a circuit diagram of the main part of the inverter 400, which includes capacitors C ₁ and C ₂ connected to a DC intermediate circuit, and semiconductor switching elements S _{1 to} S ₆ such as IGBTs connected in a three-phase bridge, A desired voltage is output by PWM control.
In FIG. 3, the voltage between the positive and negative buses of the DC intermediate circuit is e _dc (the potential at the connection point between the capacitors C ₁ and C ₂ is 0, the potential of the positive DC bus is + e _dc / 2, the negative side The potential of the DC bus is _-edc / 2). Further, the voltages of the AC output terminals U, V, and W are set as v _u , v _v , and v _w , respectively.

FIG. 4 shows the U-phase output voltage command v _u ^* of the inverter 400 and the waveform of the carrier triangular wave, respectively, during normal sine wave modulation. Here, the U-phase voltage command v _u ^* in FIG. 4 is the maximum.
From FIG. 4, since the peak value of the U-phase voltage command v _u ^* is e _dc / 2, the output voltage effective value v _urms is expressed by Equation 1.

For inverter having an input side to a diode rectifier DC intermediate circuit, since between the DC intermediate voltage e _dc input voltage effective value v _in is related to e _{dc =} √2v _in, the AC output terminal U, The line voltage effective value v _uvrms between V is expressed by Equation 2.

Therefore, the line voltage that can be output from the inverter in normal sine wave modulation is about 0.866 times the input voltage (power supply voltage).
From the above, when driving two AC motors connected in tandem with an inverter using normal sine wave modulation, the terminal voltage of each motor needs to be about 0.433 times or less of the power supply voltage. .

  Here, as a technique for improving the voltage utilization rate of the three-phase PWM inverter, two-arm modulation, trapezoidal wave modulation, triple harmonic superposition, and the like are known (for example, “Semiconductor power conversion circuit published by the Institute of Electrical Engineers of Japan” (2nd edition) ", P.124-125 etc.). When these methods are used, the output line voltage can be made equal to the power supply voltage. These methods are methods in which the phase voltage command is distorted for a certain period without making it a sine wave, thereby increasing the utilization rate of the DC voltage and making the line voltage waveform a sine wave.

For example, FIG. 5 is a waveform diagram of the U-phase and V-phase voltage commands v _u ^* and v _v ^* and the line voltage command v _uv ^* during two-arm modulation. That is, the phase of the phase voltage commands v _u ^* , v as shown in FIG. 5 is set to be always on during a half cycle of the voltage command of one phase and the zero phase component is superimposed on the voltage commands of all three phases. _{Get v} ^* .
FIG. 6 is a waveform diagram of the U-phase and V-phase voltage commands v _u ^* and v _v ^* and the line voltage command v _uv ^* during trapezoidal wave modulation. In this case, the phase voltage commands v _u ^* and v _v ^* as shown in FIG. 6 are obtained by maintaining the phase voltage commands at a constant value over a period of 60 degrees with reference to the sine wave.
5 and 6, the phase voltage commands v _u ^* and v _v ^* are not sine waves, but the line voltage command v _uv ^* (= v _u ^* −v _v ^* ) is a sine wave. Recognize.
From the above, when the output line voltage of the inverter can be made equal to the power supply voltage by 2-arm modulation, trapezoidal wave modulation, etc., the terminal voltage of the AC motor needs to be 0.5 times or less of the power supply voltage. is there.

  Note that the voltage that can be output from the inverter described above is a value under ideal conditions. In other words, the voltage that can be output from the inverter varies in consideration of the effect of dead time provided to prevent the short circuit between the upper and lower arms of the inverter, the effect of the on-voltage of the device, and the fluctuation of the power supply voltage. Therefore, it is necessary to determine the terminal voltage of the AC motor including such effects and the effects of current distortion.

Next, the windings of the electric motors 101 and 201 will be described.
As shown in FIG. 2, the first motor 101 side does not perform star connection or delta connection, and uses one end of each phase winding U1, V1, W1 as an input terminal and the other end as an output terminal. On the other hand, the second electric motor 201 side is connected in a star connection by connecting the windings U2, V2, W2 of each phase at a neutral point. Note that the phase sequence of the windings of the electric motors 101 and 201 is reversed as shown in FIG.
With the above configuration, the two motors 101 and 201 that are tandemly coupled can be driven by the single inverter 400. For this reason, it is possible to reduce the cost as compared with the case where a drive device is provided for each motor, and it is possible to suppress the occurrence of cross current by connecting the windings of each motor in series for each phase.

In this embodiment, it is necessary to reverse the phase order of the windings of the electric motors 101 and 201, but this point can be improved by a second embodiment to be described later.
Furthermore, in the first embodiment, the phases of the induced voltages of the electric motors 101 and 201 need to be matched. If these phases do not match, if the same current flows through both motors 101 and 201, there is a possibility that the output torque of each motor 101 and 201 will be different and the required output cannot be obtained. In order to prevent this, it is only necessary to mark the rotating shafts 102 and 202 of the electric motors 101 and 201, and combine these marks together.

Next, FIG. 7 is an overall configuration diagram of an electric motor drive system according to a second embodiment of the present invention.
In the present embodiment, the two electric motors 101, 210 are provided so that the windings are provided with the same stator and the winding input terminals 111, 211 are arranged on the right side, for example, as shown in FIG. 201A is configured. 7 corresponds to a state in which the rotating shaft 202 of the second electric motor 201 in FIG. 1 protrudes to the opposite side (left side in FIG. 1) and is connected to the load 300. Thereby, the structure which reversed the phase sequence similarly to FIG. 9 can be obtained using the two electric motors 101 and 201A having the same winding method.
Therefore, the two electric motors 101 and 201A coupled in tandem can be operated without using different types of stators with different winding methods, which can contribute to cost reduction.

In each of the above embodiments, the AC motor to be driven is an SPM motor having a permanent magnet on the rotor surface or an IPM motor having a rotor inside, regardless of the presence or absence of a speed sensor, a position sensor, or the like. Any of them may be used, and the kind of permanent magnet (rare earth magnet, ferrite magnet, etc.) is not particularly limited.
Furthermore, the winding method of the AC motor may be distributed winding in addition to concentrated winding as shown in FIG.

101, 201, 201A: electric motor 102, 202: rotating shaft 111, 211: winding input terminal 112: winding output terminal 300: load (coupling)
400: Three-phase inverter 501, 502: Cables U1, V1, W1, U2, V2, W2: Windings U1 _in , V1 _in , W1 _in , U1 _out , V1 _out , W1 _out , U2 _in , V2 _in , W2 _in : terminals C1, C2: capacitor S ₁ to S _6: semiconductor switching elements U, V, W: AC output terminal

Claims (2)

In a motor drive system for driving n (n is an integer of 2 or more) AC motors by one power converter,
Tandem coupling of n AC motors capable of applying a terminal voltage of 1 / n or less of the voltage that can be output from the power converter, and connecting the windings of these AC motors in series for each phase, An electric motor drive system characterized by matching the phases of induced voltages of all AC electric motors. In the electric motor drive system according to claim 1,
The rotating shafts of two AC motors having the same winding method for the stator windings are connected coaxially via a load, and the phase sequence of the windings of each motor viewed from the load is reversed. An electric motor drive system characterized by being oriented.

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