JPH07114560B2 - Induction motor instantaneous torque and magnetic flux control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control system at the time of sudden acceleration of a start among torque and magnetic flux control systems of a three-phase induction motor by a variable voltage, variable frequency PWM inverter. is there.

(Prior Art) The basic operation of the instantaneous torque and magnetic flux control system of the induction motor according to the present invention is described in the journal B of the Institute of Electrical Engineers of Japan, published in January, 1986.
Vol. 106, No. 1, pp. 9 et seq. Describes it in a paper entitled "New High Speed Torque Control Method for Induction Motor Based on Instantaneous Slip Frequency Control".

The basic principle is to calculate the instantaneously generated torque as a vector product of the primary current ▲ ▼ of the induction motor and the primary magnetic flux ₁ vector represented by the space vector, and calculate the deviation between this and the torque command T ^* and the primary magnetic flux φ. ₁ and the magnetic flux command value φ ₁ ^* , select a switching pattern that optimizes the torque response of the inverter, which is tabulated in advance, and update the output voltage of the inverter every moment to instantaneously generate the instantaneous torque and magnetic flux. To control.

FIG. 2 is a block diagram of the instantaneous torque and magnetic flux control system of the induction motor which performs the basic operation as described above.
Power is then supplied to the three-phase induction motor 6 via the three-phase PWM inverter 3 via the positive bus 1a and the negative bus 1b. The control circuit 7 processes the command and the detected current and voltage signals, and generates an energization signal for the switching element of the PWM inverter 3.
Reference numeral 4 is a power switch.

The PWM inverter 3 is constructed by connecting three arms, each of which has a switching element such as a transistor that can be turned on and off and a diode, connected in anti-parallel to each other in a three-phase gret's manner. Switching S
It can be represented as u, Sv, Sw.

Current detector 5u, 5v, 5w from each output terminal of PWM inverter 3
The three-phase induction motor 6 is supplied with power via the voltage detector 2 and the voltage detector 2 is connected between the positive and negative buses on the DC side, so that each phase current and each phase voltage can be detected from these detectors and a switch state variable described later. ing.

If the primary terminal voltage and current of the three-phase squirrel cage induction motor are ▲ ▼ and ▲ ▼, respectively, and the secondary current is ▲ ▼, the voltage equation is However, the symbols ▲ ▼, ▲ ▼, and ▲ ▼ are vector displays of the quantities that have been converted on the direct and horizontal axes, that is, the d and q axes.
For example, ▲ ▼ is v _{1d for the} d-axis component and v _{1q for the} q-axis component. , And ▲ ▼ and ▲ ▼ are defined similarly. The left side of the equation represents the case where both d and q axis components are 0,
In the case of a squirrel cage rotor, the secondary voltage is as follows.

The constant in the formula is R ₁ ; Primary winding resistance L ₁₁ ; Primary inductance R ₂ ; Secondary winding resistance L ₂₂ ; Secondary inductance M; Mutual inductance _m is rotational angular velocity, p is differential operator, j is imaginary number Represents a symbol.

On the other hand, as the definition of magnetic flux, the primary magnetic flux φ ₁ is Expand the first line of the expression Substituting expressions and rearranging If you integrate both sides That is, the primary magnetic flux of the electric motor is obtained by the integral calculation of the equation.

The changeover switches Su, Sv, Sw may fall to the positive bus bar 1a side or to the negative bus bar 1b side, and do not take intermediate positions. If the former is the state 1 and the latter is the state 0, the output states of the inverter can all be expressed by the following switch state variable table.

Here, k is a number indicating the state of the changeover switch, and there are only eight of these. Also, ▲ ▼ and ▲ ▼ are the switch state variables expressed by the d and q axis components, and the actual d and q axis voltages.
v _1d and v _1q are the voltage V of the DC voltage source 1 and Multiply by Can be expressed as

This switch state variable table is shown in FIG.
The parentheses next to v ₁ indicate the states of the changeover switches Su, Sv, Sw in order, and represent the voltage vector that steps clockwise by 60 ° as k increases. Note that k = 0 and k = 7 are called zero vectors and coincide with the origin in the figure. In k = 0 and k = 7, the changeover switches Su, Sv, and Sw that determine the output of the inverter are all positive busbars.
Although there is a difference between falling to the side of 1a and falling to the side of the negative bus 1b, all the line voltages of the three-phase induction motor 6 become zero, which is the three-phase short-circuit mode.

The instantaneous torque T is the primary magnetic flux ₁ and the primary current of the formula ▲ ▼
It is calculated by the formula as the vector product of.

Where φ _1d , v _1q and i _1d , i _1q are the primary magnetic flux, respectively.
₁ and primary current ▲ ▼ to a respective component when decomposed into d, q2 axis.

Blocks 701 and 703b are blocks for calculating the primary terminal voltage ▲ ▼ from the states of the changeover switches Su, Sv, Sw and the voltage V of the current-voltage source 1 detected by the voltage detector 2, and the switch state variable table and the formula Calculated from

Block 702 is detected by current detectors 5u, 5v, 5w 3
This block converts the phase currents iu, iv, iw into the d, q2 axis components by the following equation.

This primary current ▲ ▼ is multiplied by the primary winding resistance R ₁ in block 703a, and the primary terminal voltage ▲ in block 704.
The product of the primary winding resistance R ₁ and the primary current ▲ ▼ is subtracted from ▼.

A block 705 is a block for performing integral calculation of the magnetic flux according to an equation. The d and q biaxial components φ _1d and φ _{1q of the} primary magnetic flux ₁ are obtained, and a block 706 obtains the magnetic flux vector length φ ₁ by the following equation.

Further, in block 710, as shown in the magnetic flux state diagram of FIG. 4, the rotation angle θ of the primary magnetic flux ₁ vector in the clockwise direction with reference to the d axis is 30 °, 90 °, 150 °, 210 as boundary lines.゜, 270
The control flag f.theta. Is generated as follows depending on which region is divided every 60.degree., 330.degree ..

−30 ° ≦ θ <30 °; fθ = I 30 ° ≦ θ <90 °; fθ = II 90 ° ≦ θ <150 °; fθ = III 150 ° ≦ θ <210 °; fθ = IV 210 ° ≦ θ < 270 °; fθ = V 270 ° ≦ θ <330 °; fθ = VI Fig. 5 is a state control diagram of the hysteresis comparator, in which the magnetic flux vector length φ ₁ uses the error limit Δφ with respect to the magnetic flux command value φ ₁ ^*. A control flag fφ for controlling so that φ ₁ ^* −Δφ / 2 <φ ₁ <φ ₁ ^* + Δφ / 2 is generated. That is, when the magnetic flux vector length φ ₁ increases and reaches the upper limit φ ₁ ^* + Δφ / 2, a control flag fφ = 0 for instructing demagnetization is generated, and the magnetic flux vector length φ ₁ decreases and is the lower limit. When φ ₁ ^* −Δφ / 2 is reached, a control flag fφ = 1 for instructing magnetization is generated.

Thus, the magnetic flux vector length φ ₁ is controlled by drawing a limit cycle in the direction of the arrow shown in FIG. 5, but in reality, the magnetic flux vector length φ ₁ calculated by the equation in block 706. Is subtracted from the magnetic flux command value φ ₁ ^* in block 708, and a control flag fφ = 1,0 is generated in block 711 according to the state control diagram of FIG.

The limit cycle of the magnetic flux shown in FIG. 5 corresponds to the fact that the head of the vector of the primary magnetic flux ₁ is controlled so that it always exists in the illustrated annular portion with respect to FIG.

The control flag fφ according to FIG. 5 and the control flag fθ described with reference to FIG. 4 are combined, and for example, fφ = 1, fθ = I
If the control flag of is set, the area is -30 ° <θ
Since it means the magnetization mode at <30 °, the primary magnetic flux
_The primary voltage ▲ ▼ vector to be integrated into one vector is selected from the ones having an outward component of a circle.

Block 707 the vector product between the output of block 702 and 705 is calculated by the equation, a block for calculating the instantaneous torque T, by subtracting the instantaneous torque T from the torque command T ^* at block 709, determined by the torque command T ^* and the formula In block 712, a control flag fτ is generated according to the state controller of FIG. 6 so that the difference from the obtained instantaneous torque T is suppressed within a predetermined error limit.

FIG. 6 is a state control diagram of the three-value hysteresis comparator. When the motor is running, the torque deviation T ^* -T is the upper limit value ΔT.
_{When 1} (ΔT ₁ > 0) is reached, the acceleration mode control flag f
Generate τ = 1. When the electric motor is accelerated and the torque deviation reaches the lower limit value −ΔT ₂ (ΔT ₂ > 0), a zero vector mode control flag fτ = 0 is generated, the torque is gradually decreased, and the deviation is increased again to the upper limit value ΔT ₁ When it reaches
A limit cycle in which the hysteresis loop in the upper half of FIG. 6 orbits in the direction of the arrow is drawn.

Next, when the electric motor is performing regenerative braking, a hysteresis loop in the lower half of FIG. 6 is drawn, and when the torque deviation reaches the negative lower limit value −ΔT ₁ (ΔT ₁ > 0), the mode gradually decreases. Control flag fτ = −1 is generated. After that, the limit cycle in the direction of the arrow is repeated as in the case of power running. Thus, block 712 outputs the control flag fτ = 1,0, −1.

A block 713 is a block for determining the most suitable inverter output voltage for each combination of the three control flags fθ, fφ, fτ output from the blocks 710, 711, 712, and the block shown in FIG.
These three control flags fθ, fφ, fτ control the vector length and rotation direction of the next magnetic flux ₁ .

This switching table has three control flags fθ, f
The values of the number k of the output voltage vector are shown for all combinations of φ and fτ. By referring to this switching table in the block 713 for each operation cycle, a switching signal is sent to the inverter 3 to generate a magnetic flux and torque. Is controlled.

The inverter frequency can be considered as the rotation speed of the primary magnetic flux ₁ vector in FIG. 4, but this is not given from the outside but is generated as a result of the integration of the voltage vector by the formula.

(Problems to be Solved by the Invention) As described above, torque and magnetic flux control of the three-phase induction motor by the PWM inverter is performed based on the space vector method. However, in the conventional induction motor control by the PWM inverter, voltage and frequency are controlled. Of the magnetic flux command value φ
It is controlled with ₁ ^* as a constant value.

On the other hand, the torque command T ^* can freely take a required command value within the control range, but since the current capacity of the inverter is industrially finite, in order to prevent destruction of the switching element due to excessive current, 1 Set a limit value for the next current and set 1
Because the following current is to perform more than the current limit to the gate blocking the limit value, there may not be control following the torque command T ^* Given a large command value stepwise as the torque command T ^* . In particular, when a large torque command T ^* is given in a step-like manner in order to perform a rapid start-up acceleration from a non-excitation state at the time of starting, an excessive current in which the exciting current and the torque current are superposed flows and the protection position is set to protect the switching elements of the inverter. It sometimes operated and sudden start acceleration became impossible.

Conventionally, therefore, the inverter avoids this excessive current at the time of starting by limiting the current, but the response time must be delayed because of this.

The present invention solves the above problems and enables quick response at the time of starting.

(Means for Solving the Problem) As described above, when the start-up rapid acceleration operation is performed from the non-excitation state, a problem occurs because the excitation current and the torque current are superposed. By giving φ ₁ ^* earlier in time and giving the torque command T ^* after the actual magnetic flux φ _m of the electric motor has been established to some extent, the torque can be efficiently raised in the limited current range. be able to.

FIG. 7 is a waveform chart of each part for explaining the instantaneous torque and magnetic flux control method of the induction motor according to the present invention. The starting signal S _T , the actual magnetic flux φ _m , the magnetic flux command value φ ₁ ^*, and the torque command at the time of starting. The waveform of T ^* is shown.

Conventionally, the magnetic flux command value φ ₁ ^* was given stepwise at the starting time t ₀ , but the actual magnetic flux φ _m generated by this also tried to rise in steps, so that a large inrush current was generated.

By raising the magnetic flux command value φ ₁ ^* given at the time of starting with a time constant corresponding to the time constant on the two side of the three-phase induction motor, the actual magnetic flux φ _m can be raised without generating an inrush current. The secondary time constant T _m of a three-phase induction motor is the secondary winding resistance
It is expressed by T _m = L ₂₂ / R ₂ by R ₂ and the secondary inductance L _22, and is the rising time constant of the secondary magnetic flux. Therefore, the magnetic flux command value φ ₁ ^{* is set} to zero to 2 time constant at the starting time t ₀ . T _m
At a time t ₁ after a lapse of time corresponding to the above, linearly rising up to a predetermined value φ ₁ ^{* as} shown in the figure, the actual magnetic flux φ _m is started up in a manner similar to the magnetic flux command value without causing an inrush current. You can At this time, the magnetic flux command value may not be linear but may be raised as an exponential function that rises with the secondary time constant T _m .

Experiments have shown that if the starting current is allowed to the limit of the primary current to prevent the switching element of the inverter from being destroyed, the startup may be accelerated to about 1/3 of the secondary time constant T _m. Is known to be.

Regarding the torque command T ^* as well, by not giving the torque command at the time of starting as shown in the figure, but giving the predetermined torque command T ^* at time t ₁ after the time corresponding to the secondary time constant T _m has elapsed,
It is possible to solve the above-mentioned problems occurring at the time of starting.

(Operation) In the past, when attempting to perform rapid acceleration immediately after starting, both the large exciting current component and the torque current component flow as described above, resulting in overcurrent, which is inconvenient for control. ,
By giving the magnetic flux command value φ ₁ ^* in consideration of the rising time constant of the actual magnetic flux φ _m , it is possible to quickly shift from the non-excitation state to the excitation state and suppress the pulse-shaped inrush current immediately after the start. Further, the torque control can be smoothly performed by giving the torque command T ^* at the time t ₂ after the time corresponding to the secondary time constant T _m has elapsed.

However, the response is delayed by the time corresponding to the two time constant T _m , but since the delay of the rising of the actual magnetic flux φ _m is unavoidable, it is extremely effective as a control method considering the rising of the actual magnetic flux φ _m. This is an effective method.

(Embodiment) FIG. 1 is a block diagram of an embodiment of an instantaneous torque and magnetic flux control method for an induction motor according to the present invention. The difference from the conventional example shown in FIG. Only a function generation block 714 that generates φ ₁ ^* and a blocking block 715 that blocks the torque command T ^* only at the time of starting are added, and the same parts as those in FIG. Absent.

At the time of starting, the starting signal S _T is sent to the function generating block 714, and this starting signal S _T is continuously sent during the continuous operation as shown in FIG. When the function generation block 714 receives the start signal S _T at time t ₀ , as shown in FIG. 7, the predetermined magnetic flux command value φ ₁ ^* at time t ₁ after the time corresponding to the secondary time constant T _m has elapsed ^. Then, the magnetic flux command value φ ₁ ^* that increases linearly so that it becomes constant thereafter is sent to the block 708. The development generation block 714 continues to send the blocking release signal C to the blocking block 715 while the operation is continued after the time t ₁ .

On the other hand, the torque command T ^* necessary after the start is sent to the blocking block, but the blocking block 715 is the function generating block 714.
The torque command T ^* is blocked when there is no block release signal C from the block, and the received torque command signal T ^* is sent to the block 709 as it is while the block release signal C is received. Therefore, the torque command T ^* is not given to the block 709 until the time t ₁ after the time corresponding to the secondary time constant T _m after the start, and the necessary torque command T ^* is blocked while the operation is continued after the time t _1. 70
Will be given to 9.

In this way, in this embodiment, a predetermined magnetic flux is established without starting the inrush current from the starting time t ₀ to the time t ₁ after the time corresponding to the secondary time constant T _m at the time of starting, and the time t ₁ After that, the torque can be smoothly controlled by the predetermined torque command T ^* .

In the present embodiment, the output of the blocking block 715 is set to zero from the start time t ₀ to the time t ₁ corresponding to the secondary time constant T _m , but it is very small according to the sent torque command T ^*. A torque command close to zero may be sent to block 709 during that period.

(Effects of the Invention) The conventional torque / flux control method for an induction motor based on the space vector method cannot provide a high-speed response immediately after starting. However, as in the present invention, the secondary time obtained from the circuit constant of the induction motor is used. By giving the magnetic flux command value φ ₁ ^* and the torque command T ^* at the time of starting according to the constant T _m , the current at the time of starting is prevented from becoming a problem, and after a time corresponding to the two time constant T _m has elapsed. Can realize the characteristics of instantaneous torque control and fast response.

Since the response delay of the time corresponding to the secondary time constant T _m is inevitable in any control method, the effect of the torque of the induction motor according to the present invention on the responsiveness immediately after the start of the magnetic flux control method is large. is there.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of an instantaneous torque and magnetic flux control system for an induction motor according to the present invention, and FIG. 2 is a block diagram of an instantaneous torque and magnetic flux control system for an induction motor that performs conventional basic operation. Fig. 4 is a vector diagram showing the primary terminal voltage vector, Fig. 4 is a vector diagram showing the magnetic flux state, Fig. 5 is a state control diagram of the hysteresis comparator for magnetic flux, and Fig. 6 is a state control diagram of the three-value hysteresis comparator for torque. FIG. 7 is a waveform chart of each part for explaining the instantaneous torque and magnetic flux control method of the induction motor according to the present invention. 1 ... DC voltage source, 2 ... voltage detector 3 ... 3-phase PWM inverter 4 ... power switch, 5u, 5v, 5w ... current detector 6 ... 3-phase induction motor, 7 ... control circuit 714 ...... Function generation block 715 …… Blocking block

Claims (2)

[Claims] 1. A means for calculating an instantaneous value of a magnetic flux vector by converting a voltage and a current of a three-phase induction motor into a space vector value, and a means for calculating an instantaneous value of a torque from the magnetic flux vector and the current vector. A magnetic flux comparing means for comparing the magnetic flux command value with the magnitude of the magnetic flux vector, a torque comparing means for comparing the torque command value with the instantaneous value of the torque, and a magnetic flux vector direction discriminating means for discriminating the direction of the magnetic flux vector. In the instantaneous torque / flux control method of the induction motor, which determines the optimum output voltage of the variable voltage / variable frequency inverter by judging from the outputs of the magnetic flux comparing means, the torque comparing means, and the magnetic flux vector direction judging means. When starting the phase induction motor, the magnetic flux command value is raised with a time constant corresponding to the secondary time constant of the three-phase induction motor. Instantaneous torque, the flux control system of the electric motor. 2. The instantaneous torque of the induction motor according to claim 1, wherein the torque command value is maintained at zero or a value close to zero until the magnetic flux command value reaches a predetermined value when the induction motor is started. , Magnetic flux control method.