JPH03251095A - Output voltage limiting system in vector control - Google Patents

Abstract

PURPOSE:To suppress fluctuation of flux by sustaining the exciting current when the output voltage starts to be saturated and modifying a torque current command thereby matching the current command with an actual current. CONSTITUTION:Prestage or poststage of a PWM inverter is fed back through a control voltage setting means 11 to a limiter circuit 4, an output voltage command or a detected output voltage is compared with a voltage limit set value through a limit voltage setting means 11 and when the set value is exceeded, limit value in a torque current command limiter circuit 4 is modified through PI control. Furthermore, a difference occurs between an ASR output torque command and an input torque command and the output torque is limited thus causing mismatch with the command speed. In order to suppress the flux phito be continuously integrated during an interval when the integrating term at a PI operating section is saturated, integration is prohibited thus preventing abnormality. In other words, output from the limiter circuit 4 is fed back to an ASR control section 3.

Description

[Detailed Description of the Invention] A. Field of Industrial Application The present invention relates to an output voltage limiting method during vector control.
In particular, the present invention relates to an output voltage limiting method that prevents errors in magnetic flux control and deterioration of torque response when the voltage is saturated.

B0 Summary of the Invention The present invention provides an output voltage limiting method during vector control. When the output voltage is about to saturate, the excitation current is maintained and the torque current command is changed to keep the voltage command within the output possible range. , technology that always matches the current command and actual current even when there is no magnetic flux calculation when the voltage is saturated, accurately continues the magnetic flux control required for vector control, and performs accurate torque control immediately when the voltage is out of saturation. It provides:

C9 Conventional technology Vector control is to control the secondary magnetic flux of an induction motor and the secondary current component perpendicular to it, and as a means for this, an inverter is provided to control the current and the slip frequency.

In general, vector control is performed by controlling the current, and the output voltage is adjusted based on the difference between the current command and the detected current value so that the current flows according to the command, but the power supply voltage is infinite ( Since there is a limit to the output voltage, the current according to the current command may not flow through the inverter.

In order to prevent this, conventional measures have been taken by lowering the rated voltage of the motor and setting a sufficiently large voltage margin.

However, if the motor voltage is lowered, a large amount of current must flow in order to obtain the necessary torque, which increases motor loss, which is not preferable. In addition, a motor has leakage inductance in addition to excitation inductance, and a transient voltage is required when changing the current value suddenly, but voltage saturation is likely to occur at that time. The vector control condition continues to hold as long as the current flows according to the command value, but during the period when saturation occurs, an error occurs between the current command and the actual current, and the magnetic flux fluctuates. Therefore, the vector control conditions are not satisfied and the necessary torque cannot be obtained.

On the other hand, as the magnetic flux fluctuates, the induced electromotive force changes, and as a result, a state may occur where the current coincides with the command value. If only the instantaneous value of the current is looked at, it will not be clear that the magnetic flux has fluctuated, resulting in an incorrect torque control state during the saturation period.

Since the past history is a problem, methods have been devised such as integrating the voltage component and calculating the magnetic flux density for control, and storing past current error components as information in this integral term. The problem is that it requires the means and time to do so, making the entire system large.

D1 Problems to be Solved by the Invention At present, systems that combine vector control using voltage control and current control ACR are being actively used.

However, although this method has good characteristics in an ideal state where there is no voltage saturation, current control becomes impossible when the voltage is saturated. The reason for this is that when the output voltage is limited, there is also a limit to the current that can flow, but since there is no voltage feedback in the current control calculation section and it is not possible to judge whether the voltage is saturated, it is difficult to ensure that the current matches the command value. A
This is because the integral term of CR increases the output voltage command. Furthermore, when ASR control is performed using vector control, since current tracking is not performed, the torque current command is increased to output the torque that passes the command, resulting in an increase in the slip frequency. If the slip frequency increases in a state where the current cannot follow, the magnetic flux control conditions will not be satisfied, the amplitude and phase of the magnetic flux will change, the vector control will collapse, and it will become unstable. Even if voltage saturation is eliminated in this state, the magnetic flux cannot be changed immediately, so it takes time to return to vector control conditions. That is, even short-term voltage saturation is a serious problem in vector control conditions.

The present invention was created in view of these problems, and
Even if there is no magnetic flux calculation when the voltage is saturated, the current command always matches the actual current, the magnetic flux control necessary for vector control can be accurately continued, and accurate torque control can be performed immediately when the voltage is out of saturation. The purpose is to provide an output voltage limiting method for vector control.

Means for Solving Problem E1 Countermeasures taken against voltage saturation depend on the method of detecting voltage saturation and the object of compensation.

There are three methods for detecting voltage saturation:

(1a) Based on magnetic flux detection In a system equipped with magnetic flux detection means or magnetic flux estimation means, when vector control is performed and the magnetic flux command and the detection result do not match, it is regarded as voltage saturation.

(1b) Based on voltage command The output voltage command and the voltage limit value are compared, and when the voltage command value exceeds, the voltage is determined to be saturated.

(IC) Based on voltage output detection When the zero vector period of the PWM pattern in the output voltage disappears, the voltage is considered to be saturated. There are three types of compensation as follows.

(2a) Only the amplitude of the voltage is limited while the phase 2 frequency of the output voltage remains unchanged.

(2b) The voltage is limited by leaving a voltage component necessary for maintaining the excitation current in the output voltage.

Since the voltage is divided into known dQ vectors and corrected for each component, both the voltage amplitude and phase are corrected.

(2c) Since the method of (2b) above is equivalent to limiting the torque current, when voltage saturation is detected, the value of the limiter of the torque current command is lowered.

As described above, since there are three methods of detecting voltage saturation and three types of compensation targets, they can be classified into 3×3=9 combinations as countermeasures.

The present invention provides (1b) or (IC) and (2b) among the above
or (2c), the means for solving the above problem is equipped with a detection means for detecting the saturation of the output voltage and a feedback loop for changing the torque current limiter value, and a vector In addition, when the output voltage is about to saturate, the voltage command is maintained by maintaining the excitation current and changing the torque current command. The output voltage is controlled by a vector control output voltage limiting method that keeps the voltage within an outputtable voltage range and always matches the current command and the actual current, and the detection means compares the voltage command with the limit value of the output voltage of the inverter to determine the output voltage. The feedback loop detects the saturation of the voltage, or detects the saturation of the output voltage by the phenomenon that the zero vector period of the modulation pattern of the output voltage disappears, and the feedback loop detects the amount exceeding the limit value of the voltage command as a PI secondary. Either the torque current limiter value is changed by controlling the torque current limiter value, or the torque current limiter value is calculated using an equation or convergence calculation that prevents the output voltage from exceeding the voltage limit value due to various induced electromotive force components. This is preferred.

The F1 effect detection means is a means for detecting the saturation of the output voltage by comparing the voltage command with the limit value of the inverter output voltage, or a means for detecting the saturation of the output voltage by the phenomenon that the zero vector period of the PWM pattern of the output voltage disappears. As a feedback loop to the ASR, a feedback loop or an output voltage limit value that changes the torque current limiter value by sub-controlling the amount exceeding the limit value of the output voltage command.

A feedback loop that calculates the current component that prevents the output voltage from exceeding the voltage limit value from an equation consisting of the impedance of the voltage drop component due to the motor constant, the excitation current component, the excitation impedance, and the induced power component due to the power supply frequency. Or, it is equipped with a feedback loop that calculates the torque current limit value of the torque current limiter through convergence calculation, maintains the excitation current even when the output voltage is saturated, changes the torque current command, and has a voltage range that can output the output voltage command. The current command and actual current value always match.

G. Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration diagram of an embodiment of the present invention.

In the figure, l is the motor, 2 is the rotation speed detector, 3 is the ASR control section, 4 is the limiter circuit, 5 is the vector control section, and 6 is the A
CR control section, 7 is a PWM inverter, 8 is an adder, 9 is an integrator, 10 is a current calculation means, and 11 is a limit voltage setting means.

In the figure, an ASR control section 3, a limiter circuit 4, a vector control section 5, an ACR control section 6, a PWM inverter 7,
The solid line connecting the adder 8, the integrator 9, and the current calculation means 10 is an ASR control system constructed with a voltage source inverter. In the present invention, this configuration is provided with two loop circuits shown by broken lines, and the first loop feeds back to the limiter circuit 4 from the front stage or the rear stage of the PWM inverter 7 via the limit voltage setting means 11, and outputs The voltage command or output voltage detection is compared with the voltage limit set value of the limit voltage setting means 11, and the limiter value of the limiter circuit 4 of the torque current command is changed by the amount exceeding the voltage limit set value by the PI sub-control.

In addition, in the second loop, due to loop (1), a difference occurs between the torque command of the ΔSR output and the torque command of the ACR input, and the output torque is multiplied by 11 times, so they do not match the command speed. ACRo)P The integral term of the IMW part is
In order to suppress φ that continues to interact during the saturation period, the integration is stopped or the integral gain is suppressed to a low value to prevent the integral value from becoming abnormal, and the output of the limiter circuit 4 is controlled by ASR. Feedback to Section 3.

Figure 2 shows 1. FIG. 3 is an explanatory diagram showing an example of the basic vector control shown by the solid line, and FIG. 3 is an explanatory diagram of vector control in which the loop described in the previous section is added to that state to reduce the torque current component. It is.

In Fig. 2, the current vector d is the d-axis component L(-λ
t-/rvr) and the q-axis component QTq(-t, t/M・5,
), and the voltage vector vl is a composite value of the induced electromotive force component E due to the magnetic flux and the voltage drop component 〇drop due to the motor constant R1 and Lσ. Furthermore, Δυdrop=R+
'l I +J ω+I-a fILσ-(L, -M'
/Lt). Here, if there is no feedback shown by the dotted line in Figure 1, the voltage vector will be the induced electromotive force component E due to the magnetic flux.
, and the voltage drop component Δυdrop due to R, and Lσ, the composite value V, may protrude outside the circle having a radius of the limit value V11m1t.

Here, if the first loop shown by the broken line in Fig. 1 limits only the voltage amplitude while leaving the phase of the output voltage unchanged,
Assuming that the current flows according to the command value, the voltage drop vector component Δυdrop is the same as in the case of the basic vector, but the output voltage is not vl but V as shown by the dotted line in Figure 2.
Since it is limited to I', the induced electromotive force becomes El'. That is, even if the current is followed, when the voltage is saturated, the magnetic flux will deviate. The vector control condition continues to hold as long as the current flows according to the command value, but after the error occurs for the required time and the magnetic flux shifts, there is a risk that the condition described in L may occur. History becomes an issue. As a countermeasure for this, if the voltage component is integrated and the magnetic flux density is calculated and controlled, the past current error component will be stored as information in this integral term, and no magnetic flux abnormality will occur even if the voltage is saturated. Means and time are required for magnetic flux calculation, and the entire system becomes large. In the present invention, fluctuations in magnetic flux are suppressed by controlling the current command value so that an error between the current command value and the actual current does not occur even when the voltage is saturated.

FIG. 3 is an explanatory diagram showing an example of vector control when the torque current component is reduced from the state shown in FIG. 2 using the loop of the present invention. As is clear from the figure, the torque current is 03. has decreased, so the voltage drop is reduced.
L becomes smaller, and the output voltage v1 remains within the circle of Vlim. The induced electromotive force component E remains enough to maintain the necessary magnetic flux, while the voltage vector vl changes both in voltage amplitude and phase as the torque current component a TQ decreases, as shown by the dotted arrow in FIG. They will co-change. In other words, it can be said that current tracking and magnetic flux control are maintained by limiting the output torque during a period when the voltage is insufficient.

In addition, in Figure 3, Et=　jω1　M’ (λ d t /M) It is.

The method for determining the limit value of torque component current is (1) 3rd
As shown in the figure, the value of l V+ l = VIisit is calculated.

(2) The amount of excess voltage with respect to V11m1t is controlled by PI to suppress the torque current limiter.

This example clearly has the following effects.

(1) When the voltage is saturated, the current command and the actual current can always be matched even when there is no magnetic flux calculation, and the magnetic flux control necessary for vector control can be maintained.

(2) Torque output is limited while the voltage is saturated, but even in such cases vector control magnetic flux control can be performed, and since the magnetic flux is accurately controlled, it is possible to escape from voltage saturation. When this happens, accurate torque control can be performed immediately.

H3 Effects of the Invention As explained, according to the present invention, even when there is no magnetic flux calculation when the voltage is saturated, the current command and the actual current are always matched, and the magnetic flux control necessary for vector control is maintained accurately. However, it is possible to provide a vector control output voltage limiting method that allows accurate torque control to be performed immediately upon exiting from voltage saturation.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIGS. 2 and 3 are explanatory diagrams of vector control. 1...Motor, 2...Rotation speed detector, 3...A
SR control unit, 4...Limiter circuit,...Vector control unit, 6...ACR control unit, 7...PWM inverter, 8...Adder, 9...Integrator, 10... - Current calculation means, 11... limit voltage setting means. Figure 2: Explanatory diagram of vector control; explanatory diagram of vector control

Claims (5)

[Claims] (1) Equipped with a detection means for detecting the saturation of the output voltage and a feedback loop for changing the torque current limiter value, the output torque of the motor is controlled by vector-based current control, and when the output voltage is about to become saturated, the excitation An output voltage limiting method in vector control characterized by maintaining the current and changing the torque current command to keep the voltage command within the voltage range that can be output, so that the current command always matches the actual current. (2) An output voltage limiting method in vector control, wherein the detection means according to claim (1) detects saturation of the output voltage by comparing the voltage command with a limit value of the output voltage of the inverter. (3) An output voltage limiting method in vector control, wherein the detection means according to claim (1) detects saturation of the output voltage by a phenomenon in which a zero vector period of a modulation pattern of the output voltage disappears. (4) Output voltage limitation in vector control, characterized in that the feedback loop according to claim (1) changes the torque current limiter value by performing PI control on the amount exceeding the limit value of the voltage command. method. (5) The feedback loop according to claim (1) calculates the torque current limiter value using an equation or convergence calculation that prevents the output voltage from exceeding the voltage limit value due to various induced electromotive force components. Features an output voltage limiting method in vector control.