JPH0239195B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a non-commutator motor control method, and in particular, a synchronous motor is connected to the output side of an inverter consisting of a thyristor, and AC power applied to the synchronous motor is reversed. The present invention relates to a method for controlling a commutatorless motor using a converter.

[Technical Background of the Invention] Generally, commutatorless motors perform commutation control of armature current in a normal rotational speed range by using the induced voltage of the motor. Therefore, as a thyristor converter for driving an electric motor, the natural commutation type is widely used because of its low cost and simple configuration. There are roughly two types of detection signals for determining commutation timing in such a thyristor converter. One is a signal detected through a position detector directly connected to the rotor, and the other is a signal generated from the induced voltage phase obtained by detecting the terminal voltage of the motor. Based on these signals, that is, the phase detection values, the thyristor converter adjusts the set commutation lead angle β ₀ or the effective commutation lead angle β
This gives the commutation timing. After commutation starts, it takes a certain amount of time for the armature current to completely transfer to the next phase due to the influence of the commutation reactance of the motor, and commutation is completed after a period of so-called overlap angle u. do. Generally, the commutation margin angle γ is defined as the angle from the induced voltage electrical angle at the time of completion of commutation to the angle at which phase voltages that have been commutated with each other intersect. In converters using thyristors, even after commutation of armature current ends, there is a predetermined turn-off time unique to thyristors.
t _pff , the turn-off time is within the commutation margin angle γ when the reverse voltage is applied to the thyristor.
There must be t _pff . Furthermore, the induced voltage waveform of the motor is distorted, so the commutation margin angle γ usually needs to be set to a value of around 20 degrees or more. Note that the relationship between the electrical angles described above is expressed by the following equation.

cos(β-u)-cosβ=√2・X _C・I/V _M
………(1) γ=β−u ………(2) However, X _C is commutation reactance, V _M is motor voltage, and I is DC current. Also, the motor power factor is approximately
It is expressed as cos(β-u/2).

[Problems with background technology]

In general, it is best for the system to operate electric motors where the efficiency and power factor are as high as possible.
For this purpose, it is desirable to make the commutation margin angle γ as small as possible. One example of such control is known as so-called constant commutation margin angle control, which controls the commutation margin angle γ to a constant value. It is considered a method. However, when performing such control, in order to give the effective commutation advance angle β,
From equations (1) and (2), it is necessary to determine the effective commutation advance angle β by knowing the commutation reactance value, voltage, and current values. On the other hand, the commutation reactance X _C is generally predicted at the equipment design stage, or measured and adjusted at the testing stage to determine the relationship between the load current I and the effective commutation advance angle β. However, there are problems such as the adjustment takes time and changes in characteristics due to changes in reactance value. Furthermore, in order to perform the calculation of equation (1), if this is constructed using an analog circuit, a function generator is required, which has the drawback of complicating the construction and impeding cost reduction.

[Purpose of the invention]

Therefore, an object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to automatically adjust the effective commutation advance angle to a predetermined commutation margin angle with respect to changes in the commutation reactance value and voltage of a non-commutated motor. The object of the present invention is to provide a method for controlling a commutatorless motor that makes it possible to control a commutatorless motor.

[Summary of the invention]

In order to achieve the above object, a non-commutator motor control method according to the present invention connects a synchronous motor to the output side of an inverter consisting of a thyristor, and controls AC power applied to the synchronous motor via the inverter. In the commutator motor control method, when the commutation rectance of the motor is X _c and the terminal voltage is V _M , the initial value K ₁ of the coefficient K obtained by calculation is K ₁ >√2・X _c /V _M For each commutation operation, calculate K from the average value K of K calculated over multiple past commutation operations, the output voltage phase θ of the inverter, and the commutation overlap angle u. From the commutation margin angle γ set, the set commutation margin angle γ _s , and the input current reference I ^* of the inverter, calculate K=−sinγ _s ·(γ−γ _s )/I ^* , and the result is multiple coefficients K
It is characterized in that the average value of is newly calculated, and the next effective commutation advance angle β is determined based on the calculation formula cosβ=cosγ _s −·I ^* .

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

In a commutatorless motor control method according to an embodiment of the present invention, the effective commutation advance angle β is controlled in order to obtain a predetermined commutation margin angle γ. This will be done.

Now, when controlling a commutatorless motor,
When the commutation margin angle γ is controlled to be constant, the effective commutation advance angle β and the overlap angle u change according to the DC current value I as shown in the characteristic diagram of FIG. 1a from equation (1). However, in this case, it is assumed that the voltage and frequency of the motor are constant. On the other hand, the characteristic diagram in FIG. 1b shows the change when cosβ is plotted on the vertical axis, and as is clear from equation (1), the slope of cosβ is constant with respect to the DC current I. That is, if we rewrite equation (1), it becomes as follows.

cosβ=A−KI……(3) However, A=cosγ, K=√2·X _C /V _M.
Now, let the set commutation margin angle be γ _s , and in Fig. 1b, γ is γ _s
If an ideal effective commutation advance angle β is obtained for the DC current I, cosβ has a characteristic that matches the straight line in the figure. However, in reality
The cosβ values do not match perfectly, but are above or below the straight line. When the value of cos β with respect to the DC current I is above the straight line, the actual commutation margin angle γ is smaller than the set commutation margin angle γ _s . Generally, the set commutation margin angle γ _s itself is selected as small as possible, so it is necessary to avoid selecting the effective commutation advance angle β such that it is above the straight line. That is,
Ideally, cosβ should always operate below a straight line, and should be as close to a straight line as possible.

Now, in an ideal state, the coefficient applied to the DC current I is K.
Let us consider the slope where the coefficient is K ₁ as shown in the characteristic diagram of Figure 2. In this case, the DC current value I is I ₁
cosβ is given by equation (3), and
The cosβ corresponding to the point will be given. When this effective commutation advance angle β is given, the operating characteristics are as shown by the straight line c in Figure 2, which has a slope of −K.
Then, the straight line a is translated in parallel, and the point where it intersects with I=0 becomes the operating cosγ. This can be expressed as an equation as follows.

cosβ=cosγ _s −K ₁ I ₁ =cosγ−KI ₁ (4) From equation (4), the ideal coefficient K is as follows.

K=K ₁ −(cosγ _s −cosγ)/I ₁ ………(5) The second term on the right side of equation (5) is the difference between the commutation margin angle γ and its set value γ _s , that is, Δγ=γ− If we assume that γ _s is relatively small and apply the trigonometric formula, equation (5) can be transformed into equation (6).

K=K ₁ −Δγ・sinγ _s /I ₁ ......(6) In other words, when obtaining the ideal coefficient K, Δγ and I ₁ are changed according to equation (6) for the previous coefficient K ₁ . It can be seen that it is sufficient to reduce only the relevant amount. However, in actual operation, when formula (6) itself is applied to match the ideal coefficient K, the commutation margin angle γ
Since there is a possibility that γ _s is smaller than the set value γ s, first set the initial value K ₁ that is sufficiently larger than the expected value as the value of the coefficient K, and then By repeating the correction operation using the term, it is possible to approach the ideal coefficient K within a range that does not become smaller than the set commutation margin angle γ _s .

Based on the principle explained above, the commutation advance angle is controlled in the commutatorless motor control method according to the present invention.Next, a configuration that embodies this will be explained.

FIG. 3 is a block diagram of a control system to which a commutatorless motor control method according to an embodiment of the present invention is applied. In Figure 3, a three-phase power supply 1 converts the three-phase AC power into a forward converter 2, a DC reactor 3, and an inverse converter 4.
is supplied to the electric motor 5 via. The voltage and current of the motor 5 are detected by a voltage detector 6 and a current detector 7. An overlap angle detector 8 detects an overlap angle u based on the output of the current detector 7. On the other hand, the voltage phase detector 9 detects the voltage phase θ based on the output of the voltage detector 6. Converter 10 digitally converts the DC current reference value I ^* for obtaining a desired motor speed and inputs the converted value to microprocessor 11.
The RAM 12 operates as a memory for calculations by the microprocessor 11. Gate pulse amplifier 13
performs gate control of the inverter 4 based on a signal indicating the effective commutation advance angle β from the microprocessor 11 which is the main body of calculation. The input signals to the microprocessor 11 include the overlap angle u, the voltage phase θ, and the DC current reference I ^* . On the other hand, the output of the microprocessor 11 is a commutation signal corresponding to the effective commutation advance angle β. Further, data is exchanged with the RAM 12 that stores the coefficient K.

In this configuration, an outline of the calculations performed by the microprocessor 11 will be explained below with reference to the flowchart shown in FIG. Incidentally, in FIG. 4, the flow of calculations is shown immediately after commutation starts.

First, in routine 41, the completion of commutation is checked. If the commutation is finished here, the next routine 4 is started.
2, find the value of the commutation margin angle γ, and from this calculate Δγ (= γ
−γ _s ), and the m-th coefficient K _n is determined based on equation (6). This value is stored in routine 43 at the mth address of RAM 12, which has a storage capacity of n coefficients. After this, in the RAM 12, the address, m is increased by 1, but this m is n
If this occurs, m is returned to 1 and the coefficients are sequentially stored while cyclically visiting n addresses. Next, in routine 44, the average value of the n coefficients K stored in the RAM 12 is calculated. In this case, the microprocessor 11 executes the following calculation: =1/n _o 〓 ^p=1 K _P (7). In the next routine 45, the input DC current reference value I ^* of the inverter 4 is taken in through the A/D converter 10, and the effective commutation advance angle β is calculated based on the average value of the coefficients and the equation (3). Calculate. In the next routine 46, the effective commutation advance angle β obtained in this manner is compared with the voltage phase angle θ taken in through the voltage phase detector 9. The operations of the routine 45 and the routine 46 are as follows.
This process is repeated until it is determined that the commutation timing is reached. When the commutation timing is determined from the voltage phase angle θ, the process moves to the next routine 47, where the microprocessor 11 determines the effective commutation timing for the gate pulse amplifier 13. A signal corresponding to the flow advance angle β, that is, a commutation signal is output.

After that, the flow returns to the beginning, waits for the commutation to end, and repeats the same operation.

As described above, the optimum effective commutation advance angle β is automatically determined through the flow shown in FIG. 4 using logic that is suitable for the method of determining the ideal coefficient K. Note that if a value sufficiently larger than the expected coefficient K is stored in RAM before the start of operation, a larger effective commutation advance angle β can be obtained immediately after the start of operation.
The electric motor 5 is driven, but the effective commutation advance angle gradually settles down to a predetermined effective commutation advance angle β. Note that if the commutation margin angle γ becomes smaller than the set commutation margin angle γ _s , a logic may be designed to change the coefficient K to a larger value than in the opposite case.

By the way, in the above configuration, when calculating the coefficient K, the average of two or more coefficients is taken. This is because unstable phenomena are likely to occur due to large changes in K.

In the above embodiment, a RAM is used as the storage device, but depending on the type of microprocessor, the data may be stored in the RAM or register inside the processor. Also, the calculation formula for calculating the coefficient K may be formula (5) in addition to formula (6),
Furthermore, other equivalent arithmetic expressions may be used. On the other hand, by changing the set commutation margin angle γ _s according to the speed of the electric motor 5, it is also possible to develop control such as constant commutation margin time.

〔Effect of the invention〕

As described above, according to the present invention, even if the commutation reactance value is unknown or there is a voltage change, it is possible to operate a commutatorless motor at the automatically set commutation margin angle. In addition, the effective commutation advance angle automatically changes even when the motor is in field-weakening operation, allowing safe characteristics to be obtained over a wide speed range.Furthermore, the configuration is simpler than conventional methods. A commutatorless motor control method that can be implemented with a device that does not require adjustment can be obtained.

[Brief explanation of drawings]

FIGS. 1a and 1b are characteristic diagrams showing the operating angular characteristics of a commutatorless motor, and FIG. 2 is an angular characteristic diagram for explaining a commutatorless motor control method according to an embodiment of the present invention. FIG. 3 is a block diagram of a control system to which a commutatorless motor control method according to an embodiment of the present invention is applied, and FIG. 4 is a flowchart showing the flow of calculations in the configuration of FIG. 3. 1... Three-phase power supply, 2... Forward converter, 3... DC reactor, 4... Inverse converter, 5... Electric motor, 6
... Voltage detector, 7 ... Current detector, 8 ... Overlapping angle detector, 9 ... Voltage phase detector, 10 ... Analog/digital converter, 11 ... Microprocessor, 12 ... RAM.

Claims (1)

[Scope of Claims] 1. A non-commutator motor control method in which a synchronous motor is connected to the output side of an inverter made of a thyristor, and AC power applied to the synchronous motor is controlled via the inverter. The commutation rectance is
When X _c and the terminal voltage are _VM , the initial value K ₁ of the coefficient K obtained by calculation is set to a value of K ₁ >√2・X _c /V _M , and K is set for each commutation operation. , the average value K of K calculated over multiple past commutation operations, the commutation margin angle γ calculated from the output voltage phase θ of the inverter and the commutation overlap angle u, and the set commutation margin From the angle γ _s and the input current reference I ^* of the inverter, calculate K = −sin γ _s · (γ − γ _s )/I ^* , and the resulting multiple coefficients K
A non-commutator motor control method characterized in that the average value of is newly calculated and the next effective commutation advance angle β is determined based on the calculation formula cosβ=cosγ _s −·I ^* .