JP2592537B2 - Control method of multi-stage series inverter - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control method of a multi-stage serial inverter, and more particularly, to a multi-stage serial inverter in which a plurality of inverter units each connected to a motor are connected in multi-stage in series. In the control method.

(Prior Art) FIG. 8 shows an example of a system configuration of a vehicle drive device using such a multi-stage series inverter. In the figure, 1 is a train line, 2 is a panda graph, 3 is a wheel, and 4 is a rail. A filter reactor 5 and filter capacitors 61 to 64 are connected in series between the panda graph 2 and the wheel 3, and these capacitors 61 to 64 equally divide the input voltage Vin. Also, reference numerals 71 to 74 denote inverter units constituting the multi-stage serial inverter 7. The DC side of these inverter units 71 to 74 is
~ 64 are respectively connected to both ends.

Furthermore, 81 to 84 are modes, and each inverter unit 71
7474 are connected to the AC side. In the drawing, elements on the right side of the motors 81 to 84 show a mechanical configuration. That is, gears 91 to 94 reduce the rotation speed of the motors 81 to 84. Reference numerals 101 to 104 denote wheels, and the torque of motors 81 to 84 is transmitted to these wheels 101 to 104 via gears 91 to 94.

Usually, in this type of vehicle drive device, each motor controls the current by an inverter unit to control the torque. In the case of the device shown in FIG. The inverter units 71 to 74 are controlled so that the torques of the motors 81 to 84 are made equal so that the torque is transmitted. That is, each of the inverter units 71 to 74 constituting the multi-stage serial inverter 7 includes:
The output current, that is, the motor current is controlled to be the same.

(Problems to be Solved by the Invention) Normally, when power converters such as the inverter unit are connected in series in multiple stages, an imbalance occurs in the input capacitor voltage of the power converter and the system cannot be operated. Many.

Hereinafter, the imbalance phenomenon of the input capacitor voltage in the vehicle drive device having the configuration shown in FIG. 8 will be described. For the sake of simplicity, a case where two inverter units 71 and 72 are connected in series to form a multi-stage serial inverter 7 as shown in FIG. 9 will be described.

First, the input power Pi of each inverter unit is represented by the following equation.

_{Pi = k · φ · I m} · N m ... (1) where k: coefficient phi: motor flux I _m: motor current N _m: motor speed _{also, P i = VI i ... (} 2) where V _i : Capacitor voltage I _i : Inverter unit input current.

Therefore, I _i = P _i / V _i = k · φ · I _m · N _m / V _i (3) Furthermore, the capacitor voltage V _i is expressed by the following equation.

V _i = V _i0 + (1 / C) · ∫Ic · dt (4) where Ic: capacitor current V _i0 : capacitor initial voltage.

 First, the operation during the power running operation of the motor will be described.

In Figure 9, k of the motors 81 and 82, phi, I _m, if there is deviation in any or all of the N _m is deviation in the input power P _i1, P _i2 of the inverter unit 71 Occurs. If the relationship is P _i1 <P _i2 , then I _i1 <I _i2 and the capacitor 6
The currents of 1,62 are I _c1 > I _c2 .

If there is such a deviation in the capacitor current, Vi ₁ > Vi ₂ from the equation (4), and unless I _c1 = I _c2 = 0, the deviation of the capacitor voltage increases with time. Also,
As shown in equation (3), since I _i and V _i are in inverse proportion, V → large, I _i → small, I _c → small, V _i → large, I _i → small,. Once the balance is lost, it becomes divergent.

Furthermore, k of each motor 81,82, φ, I _m, even if no deviation is the N _m, if there is a deviation in the capacitor initial voltage, V _i → large as above, I _i → small, V _i → large, I _i → small, ... (V _i → small, I _i
→ Large, I _c → Small, V _i → Small, I _i → Large,...), And once the balance is lost, the state is also divergent.

As described above, the present system is essentially an unstable system, and needs to be controlled so that the capacitor voltage does not become unbalanced.

 Next, the operation during the regenerative operation of the motor will be described.

Here, k of the motors 81 and 82, phi, when there is deviation in any or all of the I _m, N _m is the inverter unit 7
The input power P _i1 of 1,72, the deviation occurs in the P _i2. The relationship is -P
_i1 <-I _i1 <-I _i2 becomes in the case of -P _i2, the capacitor current is I _c1 <I _c2. In this case, V _i → large, I _i → small, I _c →
Small, V _i → small,... Converge to a stable state without divergence. However, the imbalance of the capacitor voltage corresponding to the deviation of the input power occurs as in the case of the power running operation.

The present invention has been proposed in order to solve the above-described problems. An object of the present invention is to control each inverter unit so as to correct the current of a motor connected to each inverter unit, and to adjust the capacitor voltage. It is an object of the present invention to provide a control method of a multi-stage series inverter that enables stable operation by eliminating the balance.

(Means for Solving the Problems) In order to achieve the above object, the present invention relates to a multi-stage serial inverter configured by connecting a plurality of inverter units each having a motor connected thereto in series, and During operation, when the input voltage of the inverter unit is higher than the reference value, the current command of the motor connected to the inverter unit is made larger than the reference value, and
When the input voltage of the inverter unit is lower than the reference value, the current command of the motor connected to the inverter unit is made smaller than the reference value, and during the regenerative operation of the motor, the input voltage of the inverter unit becomes lower than the reference value. When it is high, the current command of the motor connected to the inverter unit is made smaller than the reference value, and when the input voltage of the inverter unit is lower than the reference value, the current command of the motor connected to the inverter unit is made Each current command is supplied to an inverter unit control circuit to be larger than a reference value to control each inverter unit.

(Operation) According to the present invention, during power running operation of the motor, the capacitor voltage with the larger input power of the inverter unit decreases and the capacitor voltage with the smaller input power increases, so that the motor current with the lower capacitor voltage is reduced. To reduce the input power and increase the motor current with the higher capacitor voltage to increase the input power. Therefore, if the inverter units are connected in series in two stages, the capacitor voltage is balanced when I _i1 = I _i2 (that is, I _c1 = I _c2 = 0).

Also, during regenerative operation, the capacitor voltage of the inverter unit with higher input power becomes higher and the capacitor voltage of lower one becomes lower. Control is performed so as to increase the input power by increasing the motor current of the lower voltage. Therefore, as described above, I _i1 = I
_{When i2} (that is, _Ic1 = _Ic2 = 0) is reached, the capacitor voltage is balanced.

Thus, in any of the power running operation and the regenerative operation, the device can be operated in a state in which the input capacitor voltages of the inverter units are automatically balanced.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a control circuit used in a first embodiment of the present invention together with a main circuit of an inverter. This embodiment is directed to a multi-stage serial inverter 7 composed of inverter units 71 and 72 connected in series in two stages as in FIG. In the figure, 201 is a balance control circuit corresponding to the inverter unit 71, 202 is a balance control circuit corresponding to the inverter unit 72, 301, 302
Is a control circuit of each of the inverter units 71 and 73.

Here, the balance control circuits 201 and 202 are configured as follows. That is, in the balance control circuits 201 and 202, 2011 and 2021 are the power running pattern circuits, and 2012 and 2022 are the regenerative pattern circuits.
_i1, V _i2 and select the output of either of the pattern circuit by the current command i _m ^* switching variable device to determine the operating mode of the power running / regeneration from 2013,2023 device, the current command so I _m1 ^*, I _m2 It is configured to output to the inverter unit control circuits 301 and 302 as ^* .

FIGS. 2 and 3 show the balance control circuit 201 (the same as in FIG. 2).
02 is the same) two the effect of the current command i _m ^*,
are those indicated for i _m ^{* ',} FIG. 2 pattern example of the balance control at the time of power running, FIG. 3 is a pattern example of a balance control during regeneration.

Next, the operation of this embodiment will be described. In Figure 1, the current command i _m ^* and the inverter unit of the apparatus 71,7
Voltage feedback V _i1 of the second input capacitor 61, 62, V _i2 is input to the balance control circuit 201, FIG. 2, the current command I _m1 ^* calculated by the pattern shown in Figure ^3, i _{m @ 2} ^* the operation mode Are output in accordance with.

Here, the balance control circuit 201 and 202, following I corresponding to the arithmetic expression _m1 ^*, I _{m @ 2} ^* is output.

Powering ^{_{I m1 * = A 1 + B}} 1 × V i1 + i m * I m2 * = A 1 + B 1 × V i2 + i m * regenerative ^{_{I m1 * = A 2 -B 2}} × V i1 + i m * I m2 * = A _{2 -B 2 × V i2 + i} m * _{Note, a 1, a 2, B} 1, B 2 are coefficients, these coefficients and the operator is stored in each pattern circuits 2011,2012,2021,2022 I have.

Next, FIG. 4 shows the operating points of the inverter units 71 and 72 on the same figure to explain the operation of the balance control circuits 201 and 202 during power running. In the initial state, the voltage of the capacitor 61 is _Vi1 and the voltage of the capacitor 62 is _Vi2.
When (V _i1 > V _i2 ), the balance control circuit 201 outputs the fourth
I _m1 ^* shown in the ^figure, the balance control circuit 202 is output I _{m @ 2} ^*. At this time, as shown in the figure, since _Im1 ^* > _Im2 ^* , the capacitor voltage _Vi1 decreases and _Vi2 increases. As a result, the operating point moves as drawn by the arrow in the figure,
Balance at the point of _Im1 ^* = _Im2 ^* . Usually, the above (1)
Since there are deviations in the motor rotation speed N _m , the motor magnetic flux φ, the coefficient k, and the like shown in the equations, a deviation is generated between I _m1 ^* and I _m2 ^* by an amount for correcting these deviations and balance is achieved.

Therefore, when I _i1 = I _i2 , the voltages V _i1 and V _i2 of the capacitors 61 and 62 are balanced.

FIG. 5 shows the operation of the balance control circuits 201 and 202 during regeneration. At the time of regeneration, since _Im1 ^* > _Im2 ^* , initially _Vi1 <V
_Since the capacitor voltage V _{i1 in} the relation of _{i 2} increases and V _i2 decreases, the same balance as in power running is _achieved .

Next, FIG. 6 shows a second embodiment of the present invention in which the fluctuation of the input voltage is considered. In this embodiment, the sum of the capacitor voltages V _i1 and V _i2 added by an adder 501 is used as an average value circuit 40.
The signal is input to each of the pattern circuits 2011, 2012, 2021, and 2022 via 0, and the voltage fluctuation of the capacitors 61 and 62 is corrected. Thus, even if the input voltage (capacitor voltage) changes from _Vi1 to _Vi1 'as shown in FIG. 7, it is possible to correct the motor current command _Im1 ^* so that it does not change.

 The pattern at this time is represented by the following equation.

Powering ^{_{I m1 * = B 1 × (}} V i1 -V ia) + i m * I m2 * = B 1 × (V i2 -V ia) + i m * regenerative ^{_{I m1 * = -B 2 × (}} V i1 -V ia ^{_{) + i m * I m2 *}} = -B 2 × (V i2 -V ia) + i m * However, V _ia is the mean value of the capacitor voltage, whose value is expressed by _{(V i1 + V i2) /} 2 .

Although not described in detail, also in this embodiment, the operation of the balance control circuits 201 'and 202' allows the capacitor voltages _Vi1 and _Vi2 to be balanced both during power running and during regeneration.

Note that the average value V of the capacitor voltage in this embodiment is
Instead of _ia , the input voltage of the device (V _{in in} FIG. 9) may be used.

Further, each of the above-mentioned execution instructions is for the case where the inverter units are connected in two stages in series, but the present invention can be generally applied to a multi-stage serial inverter in which a larger number of inverter units are connected in series. .

(Effects of the Invention) As described above, according to the present invention, the current of the motor operated by each of the inverter units connected in series in multiple stages is controlled by the balance control circuit according to the voltage of the input capacitor during the power running operation or the regenerative operation. , The voltage imbalance of the input capacitor is automatically eliminated, and the motor can be operated in a stable state.

Further, according to the present invention, a multi-stage serial inverter can be configured by serially connecting a large number of inverter units each using a low-breakdown-voltage semiconductor element to a high input voltage circuit, thereby increasing the number of inverters and reducing the cost of each inverter unit. Etc. can be met.

[Brief description of the drawings]

1 to 5 show a first embodiment of the present invention. FIG. 1 is a block diagram of a control circuit and the like, and FIGS. 2 to 5 are diagrams showing a relationship between a capacitor voltage and a motor current command. 6, FIG. 6 is a block diagram of a control circuit and the like showing a second embodiment of the present invention, FIG. 7 is a diagram showing the relationship between a capacitor voltage and a motor current command in this embodiment, and FIGS. FIG. 1 is a configuration diagram of a vehicle drive device for explaining the technique of FIG. 7 Multistage series inverter 61,62 Capacitor 71,72 Inverter unit 81,82 Motor 201,201 ', 202,202' Balance control circuit 301,302 Inverter unit control circuit 400 Average circuit 501 …… Adder 2011,2021 …… Power running pattern circuit 2012,2022 …… Regeneration pattern circuit 2013,2023 …… Switcher

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor ▲ Yoshi ▼ Haruki 1-1-1 Tanabe-Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (72) Inventor Hideaki Ishibashi Arata Tanabe, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 1-1 Fuji Electric Co., Ltd. (72) Michio Iwahori 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Fuji Electric Co., Ltd. (56) References JP-A-2-231993 (JP, A JP-A-2-299499 (JP, A)

Claims (1)

(57) [Claims] 1. A multi-stage serial inverter in which a plurality of inverter units each having a motor connected to each other are connected in series, and when the input voltage of the inverter unit is higher than a reference value during power running operation of the motor. Makes the current command of the motor connected to the inverter unit larger than the reference value, and when the input voltage of the inverter unit is lower than the reference value, sets the current command of the motor connected to the inverter unit to the reference value. When the input voltage of the inverter unit is higher than the reference value during the regenerative operation of the motor, the current command of the motor connected to the inverter unit is made smaller than the reference value, and If the input voltage is lower than the reference value, the power of the motor connected to the inverter unit Command is larger than the reference value, the control method of the multi-stage series inverters, characterized in that each current command given to the inverter unit control circuit for controlling the respective inverter units.