JP3084832B2 - Control device for brushless DC motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a control device for a brushless DC motor having a permanent magnet field, and more particularly to a regenerative braking control device.

[0002]

2. Description of the Related Art A control device for a brushless DC motor that obtains a field magnetic flux by a permanent magnet is often provided with a current control system as a minor loop control system of a speed control system or as an independent control system. Is configured as shown in FIG. 5, for example.

[0003] DC power from a DC power supply 1 is converted into a voltage output having a PWM waveform controlled by an inverter main circuit 2 and supplied as an armature current of a DC brushless motor 3. The rotor position of the motor 3 is detected by the absolute encoder 4 as a phase signal θ. The current command I _1ref is set to a multiplier of the multipliers 5 ₁ and 5 ₂ , and the multiplier 5 _1
1, 5 to ₂ of the multiplicand is a sine wave signal 120 degrees phase-shifted from one another from the sine wave generator 6. This sine wave phase is controlled according to the phase signal θ of the encoder 4.

[0004] Multiplier 5 _1, 5 ₂ of the output 3 to the motor 3
Among the phase inputs, u-phase and w-phase sine wave current commands I _u , I _w are extracted, and these current commands I _u , I _w, motor current I _u ',
The current control amplifier 7 ₁ using I _w ′ as a feedback signal,
Are proportional-integral calculation by 7 _2, the voltage command V _u of u-phase and w-phase, are taken out as V _w.

The voltage commands V _u and V _w are added by the adder 8 to generate a v-phase voltage command V _{v at} the output of the adder 9. These voltage commands V _u , V _v , V _w are used as comparison inputs of comparators 9 ₁ , 9 ₂ , 9 ₃ as a PWM generation circuit, and are supplied with a triangular wave signal from a carrier generator 10 as a reference for comparison. Sine-wave approximated PWM waveforms are taken out from the outputs of 9 _{1 to} 9 ₃ , and these PWM waveforms are converted into gate signals of respective phases of the inverter main circuit 2, amplified by the gate circuit 11, and are switched by the phase switch elements of the inverter main circuit 2. Drive signal.

With such a configuration, the current control system controls the torque of the motor 3 by performing feedback control of the motor current.

Here, the DC power supply 1 has a configuration obtained by a rectifier from an AC power supply, a configuration in which a battery (stand-by power supply) for uninterruptible power supply is provided, and a configuration having only a battery power supply. Among them, those with batteries in the DC power supply use regenerative braking that returns energy to the power supply side during braking,
In the illustrated configuration, regenerative braking is performed by giving a negative command to the current command _I1ref .

[0008]

In the conventional regenerative braking,
Because it controls the braking Doruku by the current command I _1ref, there is a problem that exceed the maximum allowable regenerative electric power by setting the current command I _1ref to obtain the desired braking torque. This maximum allowable regenerative power is determined mainly by the maximum allowable charging current of the battery and the battery voltage at that time.
The battery voltage fluctuates greatly depending on the degree of discharge, and the current command I
Simply setting a fixed limiter value of 1 _ref may cause overcharging of the battery beyond the maximum allowable regenerative power, or regenerating with insufficient braking torque or poor power efficiency.

In addition to the above-mentioned problems, the regenerative energy decreases in the low-speed range of the motor 3, so that depending on the setting of the braking torque, reverse braking is performed by supplying energy from the power supply side to perform braking. In this case, the regenerative braking generates heat of the motor, energy loss of the battery, and the like, resulting in regenerative braking that is less efficient than mechanical braking.

It is an object of the present invention to provide a control device that makes regenerative power to a DC power supply equal to or less than an allowable value, prevents reverse braking, and achieves efficient regenerative braking.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention compares a current command of a current supplied from an inverter to a brushless DC motor with a detected value thereof and controls the inverter output voltage by a sine-wave approximate PWM control. has a current system that, in the control device for a brushless DC motor to perform regenerative braking and the drive of the DC motor by switching the current command of the current control system in positive and negative, and the DC voltage E _d and the motor rotation speed ω and the motor of the inverter From the characteristic coefficients of the inverter, the currents I _1a and I _1b are calculated by the following equations.

[0012]

(Equation 3)

[0013]

(Equation 4)

Here, E _d : inverter DC voltage I _d : inverter DC current L ₁ : leakage inductance of motor winding K _v : motor induced voltage constant K ₂ : inverter loss coefficient K ₁ : calculation means obtained from motor loss coefficient The current I during regenerative braking of the motor.
Characterized in that a limiter means for limiting the current command in the range of ₁ a and I ₁ b.

[0015]

When the electric braking is performed by the motor, there are a region operated by the regenerative braking and a region operated by the reverse rotation braking. In the present invention, the regenerative braking is performed within the limited region by the regenerative electric power and not entering the reverse rotation braking region.

First, an area where regenerative braking is limited by the maximum allowable regenerative power will be described.

The power relation during regeneration, the voltage showing the respective portions in FIG. 1, when a _{current, 3E 0 I 1 = W IM} + W INV + E d I d ····· (1) where, W _IM: motor loss E _d : DC voltage W _INV : Inverter loss I _d : DC current E ₀ : Motor induced voltage (phase voltage) I ₁ : Motor current Among them, the motor loss W _IM is mainly a loss proportional to the square of the current such as its primary resistance, and the inverter loss is almost proportional to the current. Therefore, if these losses are loss coefficients K ₁ and K ₂ , respectively, W W _IM = K ₁ I ₁ ² (2) W _INV = K ₂ I ₁ (3)

[0018] than the above-mentioned (1) to (3), becomes a relation of ^{_{K 2 I 1 2 + (K}} 2 -3E 0) I 1 + E d I d = 0 ····· (4), which Solving for motor current I ₁ gives

[0019]

(Equation 5)

## EQU1 ## Here, the motor induced voltage E ₀ and the torque T are represented by the following relationship: E ₀ = K _V ω (6) T = K _i I ₁ (7) where K _v : induced voltage Constant _Ki : torque constant ω: Motor rotation speed (rotational angular velocity).

Therefore, the motor current I _1LIM obtained by substituting the maximum allowable charging current into the regenerative current I _d to the battery 1 is obtained from the equation (5), and the motor is limited by the maximum allowable regenerative power by limiting the motor current I _1LIM. it is possible to control the current I _1. At this time, the current I _1LIM is a DC voltage (battery voltage) E _d
By a a function of the motor rotation speed omega, it controls the motor current I _1LIM according to the rotation number omega these voltage E _d,
The regenerative power to the battery is set within an allowable value, and the desired braking torque T (= K _i I ₁ ) can be obtained within the allowable value.

Next, the reverse braking region will be described. The maximum current that enables regeneration is the current that flows when the motor winding is short-circuited on the inverter 2 side. When the braking torque is increased by increasing the current more than this, the vehicle enters the reverse rotation braking region, and power is supplied from the battery 1 to the motor 3. Therefore, the reverse rotation braking region is bounded by the short-circuit current of the motor 3.

At a low speed, the short-circuit current of the motor has a winding resistance _Ra.
Determined by the inductance L ₁ and the inverter loss leak and. Among them, the equivalent resistance R _a1 for one phase including the inverter loss of the aforementioned (2), and obtained from equation _{(3), R a1 = (W IM +} W INV) / 3 · I 1 2 = (K 1 _{+ K 2 / I 1) /} 3 becomes ..... (8). On the other hand, the voltage balance equation when the terminals of the motor are short-circuited by turning on the element of the inverter 2 is as follows: E ₀ = R _a1 I ₁ + jωL ₁ I ₁ (9) If by substituting the value (8) obtains the motor current I ₁ by the following equation.

[0024]

(Equation 6)

Accordingly, by setting the motor current value I ₁ operating in the regenerative region at each rotational speed ω as the limit value in accordance with the above equation (10), operation in the reverse rotation braking region can be avoided or torque control can be performed.

From the above, according to the present invention, the regenerative power is limited to an allowable value by limiting the current command according to the equation (5), and the reverse braking region is limited by limiting the current command according to the equation (10). Limit regenerative braking to avoid.

[0027]

FIG. 2 is a circuit diagram of a current control system showing one embodiment of the present invention. 5 is different from the control circuit of FIG.
It has a limiter unit 12, a braking current range calculation unit 13, and a phase angle calculation unit 14.

The phase angle calculator 14 calculates the rotation speed ω of the motor 3 by integrating the phase angle signal θ from the absolute encoder 4.

The braking current range calculation unit 13, the quality factor of the detected values and the motor and the inverter of the induced voltage E ₀ of the DC voltage E _d and the motor 3 of the motor rotation number ω and the inverter main circuit 2 described above (5) The calculation according to the formula and the formula (10) is performed, and the current limit value I _LIM is obtained from both calculation results.

The braking current range calculation unit 13 obtains the voltages E _d , E ₀ and the rotation speed ω as parameters in advance, stores this table data as table data in advance, and determines the current limiting value from the values of each parameter. A configuration in which the value I _LIM flows out of the table data may be used.

The limiter 12 takes in the signals of the current limit value I _LIM and the motor rotation speed ω from the calculation unit 13 and obtains an output in which the current command value I _1ref is limited to the current limit value I _LIM .

The limiter 12 has a rotation speed ω and a current command I.
_{Based on} the polarity of _1ref , the driving time and the regenerating time of the motor 3 are determined for each rotation direction, and the current command I _1ref is limited to the current limit value I _LIM only during rotation.

FIG. 3 shows a software configuration of the limiter unit 12. The limiter unit 12 determines whether the motor 3 is rotating forward or backward based on whether the motor rotation speed ω is positive or negative (step s1).
It is determined _whether the current command I _1ref is positive or negative when the motor 3 is _rotating forward (step s2), and similarly, _whether the current command I _1ref is positive or negative when the motor 3 is _rotating reversely (step s3).

Based on these determinations, the limiter 12 determines the driving state and the braking state of the motor 3, and determines whether or not the current command I _1ref is larger in absolute value than the current limit value I _LIM in the braking state (step s4). , S5), current command I
_1ref is when greater than the current limit value I _LIM to output a current limit value I _LIM at that time as a current command (I _1ref) '(step s6, s7). Conversely, it is the current command without limiting said current command I _1ref when the current command I _1ref is smaller than the current limit I _LIM braking state (I
_1ref ) '(step s8). Also, in the driving state of the motor 3, the current command I
_1ref is output as it is.

FIG. 4 exemplifies the operating region characteristics of regenerative braking according to the present invention. In the figure, a curve A shows a limiting characteristic from the maximum allowable regenerative power according to the equation (5), and a curve B shows a limiting characteristic from the reverse braking region according to the equation (10), which is surrounded by both limiting characteristics. The hatched area indicates the limit range of the regenerative braking. Note that the broken line C shows the characteristics at the time of driving.

[0036]

As described above, according to the present invention, the current command is limited within the range of the limit from the maximum allowable regenerative power and the limit from the reverse braking region. It is possible to prevent the deterioration due to overcharge or the like by limiting to the following, and to prevent the overheating of the motor or the power loss of the battery by avoiding the braking in the reverse rotation braking region, so that efficient regenerative braking can be obtained.

[Brief description of the drawings]

FIG. 1 is a power relation diagram during regeneration for explaining the present invention in principle.

FIG. 2 is a circuit diagram showing one embodiment of the present invention.

FIG. 3 is a flowchart of a limiter unit.

FIG. 4 is an operation region characteristic diagram of regenerative braking.

FIG. 5 is a configuration diagram of a conventional apparatus.

[Explanation of symbols]

1 ... DC power source, 2 ... Inverter, 3 ... brushless DC motor, 5 _1, 5 ₂ ... multiplier, 6 ... sine wave generator,
7 ₁ , 7 ₂ ... current control amplifier, 9 ₁ , 9 ₃ ... comparator,
10: carrier wave generator, 12: limiter unit, 13: braking current range calculation unit, 14: phase angle calculation unit.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02P 6/08

Claims (1)

(57) [Claims] 1. A current system for performing a sine-wave approximation PWM control of an inverter output voltage by comparing a current command of a current supplied from an inverter to a brushless DC motor with a detection value thereof, and setting the current command of the current control system to be positive or negative. a control device for a brushless DC motor to perform regenerative braking and the drive of the DC motor by switching the inverter DC voltage E _d and the motor rotation speed ω and the motor and the inverter of the the characteristic coefficient current I _1a, following equation I _1b [ Equation 1 (Equation 2) Where E _d : inverter DC voltage I _d : inverter DC current L ₁ : leakage inductance of motor winding K _v : motor induced voltage constant K ₂ : inverter loss coefficient K ₁ : motor loss coefficient The current I during regenerative braking
A control device for a brushless DC motor, comprising: limiter means for limiting the current command within a range of _1a and I _1b .