JPS5842718B2 - Control device for commutatorless motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a control device for a DC non-commutator motor.

In a DC type non-commutator motor, it is necessary to use an inverter to commutate the current according to the operating frequency of the motor.

To perform this commutation, a natural commutation method is used that utilizes the back electromotive force of the motor.

However, with the rudder and natural commutation method, the back electromotive force of the motor is small at the time of starting, making commutation impossible and making starting difficult.

Therefore, a so-called intermittent starting method has been proposed, in which the DC output current of the forward converter is made zero at each commutation point of the reverse converter during startup, and the reverse converter is commutated.

This intermittent starting method will be explained using FIGS. 1 and 2.

FIG. 1 is a block diagram of a control device for a commutatorless motor using an intermittent starting method.

In Fig. 1, 1 is a three-phase AC power supply, 2 is a forward converter that converts AC to DC, 3 is a DC reactor that reduces the ripples in the DC output current of the forward converter 2, and 4 is a variable frequency converter for converting DC to DC. 5 is a synchronous motor connected to the output side of the inverter 4; 6 is a distributor J that detects the relative position of the armature of the motor 5 and the field; 7 is the rotation of the motor 5; The rotary generator 58 that detects the number is a DC current transformer that detects the DC current,
9 is a current control circuit that controls the current by outputting a phase command signal according to the deviation between the current command value and the actual value detected by the current transformer 8; 10 is a current control circuit that controls the current according to the deviation output of the mold groove control circuit 9; A pulse phase shifter 11 that controls the firing phase of the forward converter 2 and makes its output voltage variable, detects the zero point of the DC current and outputs a zero current signal, and at the same time the speed signal of the rotating electric machine 7 reaches the set value. Then, a starting control circuit 12 generates a γ switching signal to switch the control advance angle r, and a starting control circuit 12 determines the firing timing of the inverter 4 based on the position signal of the distributor 6, and also applies an intermittent command pulse to the current control circuit 9. The logic circuit 13 is a gate output circuit which provides a firing pulse to the inverter 4.

Since the operation of such a configuration is well known, detailed explanation will be omitted, and the phase relationship between commutation and current intermittent in the conventional inverter will be briefly explained.

In order to maximize the output torque at startup, the control advance angle γ is set to γ.
The force where =:=O° is also shown in FIG. 2 as γ=O°.

U, V, and W indicate the phase voltage of the motor 5, and AlB and C indicate the position signal of the distributor 6, and the width of this position signal is 18 in electrical angle.
0°, and each has a phase difference of 120°.

UP-WP is the positive side thyristor UP, VP of the inverter 4,
WP gate signal, UN-WN is negative side thyristor UP
, VN, and WN gate signals.

The width of these gate signals is 120 degrees in electrical angle, and the commutation period on the positive and negative sides is 60 degrees in electrical angle.

The logic circuit 12 generates an intermittent command pulse at the rising edge of the gate signals UP, VP, .

Therefore, the intermittent command pulse is generated every 60 degrees in electrical angle.

The current control circuit 9 changes the phase command signal number as shown in the figure using intermittent command pulses.

Thus, the pulse phase shifter 10' changes the firing phase of the forward converter 2 to make the DC output current zero.

After the DC current becomes zero, the inverter 4 commutates.

Then, the intermittent command pulse disappears after a time equal to or longer than the turn-off time of the thyristor.

Therefore, the motor currents IU to Iw are as shown in the figure,
It becomes zero every 60 degrees in electrical angle.

Thereafter, at time t1, the back electromotive force of the motor 5 is established, and the back electromotive force enables commutation of the inverse converter 4.

That is, natural commutation takes place. When natural commutation occurs, the control advance angle γ is set to γ>O, but the figure shows the case of operation at γ=60°.

゛As is clear from Fig. 2, the commutation of the inverter 4 is 60
The current flows continuously.

Note that switching to natural commutation is based on the motor speed and the set speed (the speed at which back electromotive force is established), which is usually 5 to 10% of the motor rated speed.
This is done by comparing the starting control circuit 11.

Although the control is performed in this manner, the following problems exist when the current is interrupted.

That is, since the current is interrupted every 60 degrees in J electrical angle, the number of interruptions until natural commutation occurs is increased.

Therefore, the average value of the load current becomes smaller and the acceleration torque also becomes smaller.

In other words, the time width t of the intermittent command pulse.

is determined by the thyristor turn-off time and current reduction time (determined by the value of the DC reactor DCL, etc.).
and is always constant regardless of motor speed.

On the other hand, the intermittent period T becomes smaller as the motor speed increases, and the ratio between to and T becomes t.

/T increases as the motor speed increases.

Therefore, the average value of the DC current becomes smaller as the number of interruptions increases, and the motor torque also decreases.

Furthermore, the DC current is switched on and off regardless of the firing phase of the forward converter, that is, the power supply voltage phase.

Therefore, the input current of the forward converter becomes unbalanced, and the power transformer receives DC bias.

The amount of DC biased magnetism increases as the number of times the current is interrupted increases.

Therefore, the capacity of the power transformer must be increased for starting, which is economically disadvantageous.

The present invention has been made in response to the above-mentioned problems, and its purpose is to reduce the number of current interruptions, increase the output torque of the motor, and reduce the amount of DC biased magnetism in the power transformer. An object of the present invention is to provide a control device for an electric motor.

The feature of the present invention is that when the number of phases of the polyphase inverter is n, the positive side thyristor of one phase of the polyphase inverter and the negative side thyristor of a different phase of the polyphase inverter at low speed are 360' in electrical angle.
This is because the ignition control is performed so that the current is turned on at the same time and commutated at the same time by /n, thereby lengthening the intermittent cycle.

FIG. 3 is a diagram illustrating an exemplary logic circuit according to the present invention.

In Fig. 3, A, B, and C are the 6th position signals of the distributor shown in Fig. 1, and each is 1800 width in electrical angle.
It has a phase difference of 20°.

X is an intermittent command signal that becomes high level when the current is intermittent,
Y is a continuous command signal that becomes high level when the current is continuous.

Switching between the signals X and Y is performed by comparing the speed feedback signal with a set value.

14 to 16 are inverting circuits, 17 to 31 are AND circuits, 32
37 is an OR circuit.

Next, its operation will be explained with reference to FIG.

The position signals A, B, and C are inverted by inverting circuits 14 to 16 to become signals A, 10, and 16.

Position signals A, BC and inverted signals A, B, C are applied to AND circuits 17-22, respectively.

Then, the AND circuit 17 generates a signal E which is the AND of A and B (7), and the AND circuit 18 generates a signal F of B and C.
Also, the C and K signals G are obtained by the AND circuit 19.

These signals E, F, and G are guided to AND circuits 23-25.

When the current is interrupted, the OR circuits 32 to 37 generate six gate signals UP-WP and UN-WN as shown.

When the current is interrupted, the gate signals UP, ■NJV□P, WN, wp and UN are generated simultaneously and become a signal of 120 degrees in electrical angle.

When the current is continuous, add A and C, B and A together with signals E, F, and G.
, C and B are added to AND circuits 20 to 22, respectively, to generate signals H1■ and J.

And signals EF, G, H, I, J and continuous command signal Y
As a result, six gate signals as shown in the figure are generated from the AND circuits 26 to 31.

This gate signal UP-WN is output via the OR circuits 32 to 37, but UP and VN, VP and WN, and WP and U
N will have a 60° phase difference.

It is clear from the relationship between the signals X and Y that the AND circuits 23-25 generate outputs when the current is intermittent, and the AND circuits 26-31 generate outputs when the current continues.

In the present invention, since the logic circuit 12 operates as described above, the gate signal of the inverter 4 is such that commutation of the positive side and negative side thyristors is performed at the same time as shown in FIG. 5, and the commutation period is The electrical angle is 120°.

Intermittent command pulses are also generated every 120 degrees in electrical angle.

This intermittent command pulse changes the phase command signal to the pulse phase shifter 10 to make the DC output current of the forward converter 2 zero.

After the DC current becomes zero, the inverter performs commutation, and the current flows after a time equal to or longer than the thyristor turn-off time.

Therefore, the motor currents IU to Iw become zero every 120 degrees in electrical angle as shown in the figure.

This operating region is indicated by the current intermittent region.

At time t1, a back electromotive force of the motor is established, and the back electromotive force enables commutation of the inverse converter.

In this current continuous region, the phase relationship and operation between the gate signal of the inverter 4 and the motor phase voltage are the same as the conventional operation.

This region is shown as a current continuous region.

FIG. 6 shows the operating states of speed, direct current, and intermittent command pulses according to the prior art and the present invention.

FIG. 6a shows the conventional case, and FIG. 6b shows the case of the present invention.

As is clear from FIG. 6, the intermittent period T becomes larger than in the conventional case, and to/T becomes smaller.

As a result, the average value of the direct current increases.

As a result, the output torque of the electric motor increases and the acceleration time can be shortened.

Further, DC bias in the power transformer provided on the power source side can also be reduced by reducing the number of interruptions.

As explained above, according to the present invention, the number of interruptions can be reduced, so the output torque can be increased, and the DC bias of the power transformer can also be reduced.

Furthermore, when the current is interrupted, the responsiveness of the control system is worse than when it is continuous, and the more the number of interruptions is, the worse it gets, but the responsiveness can be improved by reducing the number of interruptions.

Although the above description has been made regarding the case where the current intermittent state is started, it goes without saying that the intermittent current state is also carried out in the same manner when intermittent operation is performed at a low speed (approximately 10% of the rated speed).

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a control device for a non-commutated motor, FIG. 2 is a waveform diagram for explaining conventional operation, FIG. 3 is a configuration diagram showing an example of a logic circuit according to the present invention, and FIG. is a diagram explaining the operation, and FIG. 5 is a waveform diagram explaining the operation according to the present invention.
FIG. 6 is a waveform diagram showing the present invention and a conventional control method. Explanation of symbols, 2... Forward converter, 3... DC reactor, 4... Inverse converter, 5... Periodic motor, 6...
Distributor, 7... Rotary generator, 9... Current control circuit,
10... Pulse phaser, 11... Starting control circuit, 1
2...Logic circuit.

Claims (1)

[Claims] 1. A forward converter that converts alternating current into direct current, a polyphase inverse converter that converts the direct current output of the forward converter into variable frequency alternating current, and an output side of the polyphase inverse converter. The synchronous motor includes a connected synchronous motor, a distributor that detects the rotor position of the synchronous motor, and a logic circuit that provides a gate signal to the polyphase inverter based on the position signal of the distributor. At low speeds, the DC output current of the forward converter is made zero at every commutation point of the multiphase inverse converter. In the control device for a non-commutator motor as described above, when the number of phases of the polyphase inverter is n, the logic circuit operates on the positive side of one phase of the polyphase inverter when the synchronous motor is at low speed. A control device for a commutatorless motor, characterized in that a gate signal is applied so that a thyristor and negative-side thyristors of different phases conduct at the same time by 360°/n in electrical angle and commutate at the same time.