JP4736116B2 - Electric power steering control device and method - Google Patents

Description

  The present invention relates to a power steering control apparatus and method for driving an electric motor that generates an auxiliary steering torque based on a steering torque.

  As an auxiliary steering device for an automobile, an electric power steering device using the torque of an electric motor is used. This power steering device includes a torque sensor that detects a steering operation by a driver, a power steering control device that calculates an auxiliary steering force based on a detection signal from the torque sensor, and rotational torque based on an output signal from the control device. An electric motor that is generated and a reduction gear that transmits rotational torque to the steering mechanism are provided.

  The above-described power steering control device is configured by a computer including a CPU, a memory, and the like, and can execute a plurality of processes by executing a predetermined software program. Software processing includes current command value calculation processing for calculating a current command value by inputting signals from a torque sensor and a vehicle speed sensor, and a PWM (pulse width modulation) signal for driving a three-phase motor based on the current command value. Current control processing to be generated, rotation angle calculation processing for calculating angular velocity and angular acceleration based on the rotation angle of the motor detected by a resolver, etc., compensation control processing for performing various compensation controls for current command values based on angular velocity, etc. Etc.

  Further, vector control is used in the above-described current control process. In this vector control, the excitation current and the torque current can be controlled independently as in the case of the DC motor, and the three-phase motor can be controlled with high accuracy. An example of a conventional power steering control device using vector control is shown in FIG. This power steering control device includes a current command value calculation unit 901, adders 902 and 903, PI control units 904 and 905, a three-phase-dq conversion unit 906, a PWM controller 907, current detection units 908 and 909, and a three-phase-dq. A conversion unit 910, a resolver 911, a rotation angle detection unit 912, a motor 913 for generating steering torque, and the like are provided.

  The current command value 901 has a function of calculating a d-axis current command value and a q-axis current command value based on a torque signal, a vehicle speed signal, and the like. The three-phase-dq conversion unit 906 converts the motor current value detected by the current detection units 908 and 909 into a d-axis current detection value and a q-axis current detection value, and outputs them to adders 902 and 903, respectively. The adder 902 calculates the difference between the d-axis current command value and the d-axis current detection value, and the adder 903 calculates the difference between the q-axis current command value and the q-axis current detection value. The PI control units 904 and 905 perform PI control based on the respective differences to generate the d-axis target voltage Vd and the q-axis target voltage Vq, and the dq-3 phase conversion unit 906 performs the d-axis target voltage Vd and the q-axis target voltage. Three-phase motor voltages Va, Vb, and Vc are generated based on the voltage Vq and the motor rotation angle. The PWM controller 907 outputs a drive current obtained by pulse width modulation of the motor voltages Va, Vb, and Vc to the motor 913, and generates a steering assist torque.

  In the above configuration, the current command value calculation unit 901, the adders 902 and 903, the PI control units 904 and 905, the dq-3 phase conversion unit 906, the PWM controller 907, the current detection units 908 and 909, and the 3 phase-dq conversion unit 910 Is realized by software processing, the load on the processor is large. If the control speed of the current control process is delayed in the processor, the motor current waveform is distorted, causing problems such as torque ripple, vibration, and noise. In addition, since a processor with high processing capacity is expensive, it is not always appropriate to incorporate it into a power steering control device.

  In order to solve such a problem, as described in, for example, Japanese Patent Application Laid-Open No. 2004-210289, the calculation period of the current command value calculation unit is made longer than the calculation period of the current control unit, thereby calculating the entire calculation. Devices have been devised to reduce the load. According to this apparatus, the calculation cycle of the current command value calculation unit 901 is Ta, the calculation cycle of the current control process such as the PI control units 904 and 905 is Tb, the calculation cycle of the voltage control process such as the dq-3 phase conversion unit 906 and the like. Is set to Tc, the calculation cycle of each part is determined so that Ta> Tb = Tc. That is, this device is intended to reduce the load of the entire process by avoiding the above-described problem by making the calculation cycle Ta of the current command value calculation process longer than other calculation cycles.

  However, the dq-3 phase conversion process and the 3 phase-dq conversion process in the current control process require a calculation process using the rotation angle θ as a variable, and a process with a heavy load such as a reference process of a sin table is required. For this reason, even if the calculation cycle Ta of the current command value calculation unit is increased, the calculation amount cannot be reduced sufficiently.

As another prior art, an apparatus described in Japanese Patent Laid-Open No. 2003-267237 has been devised. The purpose of this apparatus is to further reduce the load of the entire process by making the calculation cycle Tb of the current control process longer than the calculation cycle Tc of the voltage control process. However, similar to the above-described prior art, an operation including the rotation angle θ as a variable must be executed, and the processing load cannot be reduced sufficiently.
Japanese Patent Laid-Open No. 2004-210289 JP 2003-267237 A

  The present invention has been made in view of the above-mentioned problems, and the problem to be solved by the present invention is to provide an electric power steering control device and method capable of reducing the calculation load while suppressing waveform distortion in the control waveform. There is to do.

  In order to solve the above-described problems, the present invention provides a current command value calculation unit that calculates a current command value based on a steering torque applied to a steering, a PWM drive current supplied to a motor for generating steering assist torque, Based on the difference from the current command value, a voltage command value calculation unit that calculates a voltage command value every calculation cycle T1, and the rotation angle Δθ of the motor in a calculation cycle T2 shorter than the voltage command value and the calculation cycle T1 And calculating a duty command value for calculating the duty command value of the PWM drive current by accumulating the voltage command value deviation in the voltage command value every calculation cycle T2. A part.

The calculation cycle T1 is an integral multiple of the calculation cycle T2.
Further, the duty command value calculation unit is based on the three-phase voltage command values Va, Vb, Vc and the rotation angle Δθ calculated for each calculation cycle T1, respectively.
ΔVa = ((√3) / 3) × Δθ × (Vc−Vb),
ΔVb = ((√3) / 3) × Δθ × (Va−Vc),
ΔVc = ((√3) / 3) × Δθ × (Vb−Va),
The voltage command value deviations ΔVa, ΔVb, ΔVc expressed by the following are calculated for each calculation cycle T2.

  According to the present invention, the current command value calculator calculates a current command value based on the steering torque applied to the steering, and the voltage command value calculator calculates the PWM drive current supplied to the motor for generating steering assist torque and the Based on the difference from the current command value, the voltage command value is calculated every calculation cycle T1. The duty command value calculation unit calculates a voltage command value deviation represented by the voltage command value calculation unit, the voltage command value, and the rotation angle Δθ of the motor in the calculation cycle T2 shorter than the calculation cycle T1. The duty command value of the PWM drive current is calculated by accumulating the voltage command value deviation in the voltage command value every calculation cycle T2.

  As described above, since the voltage command value deviation can be calculated based on the voltage command value and the motor rotation angle Δθ, a voltage command value with less waveform distortion can be obtained without requiring complicated calculation processing including a sin table. It is possible to calculate. Further, even if the calculation cycle T1 of the voltage command value calculation process with a large calculation load is made longer than the calculation cycle T2 of the duty command value calculation process, an increase in waveform distortion can be suppressed. Therefore, according to the present invention, the waveform distortion in the voltage command value can be reduced while reducing the calculation load, and problems such as torque ripple, vibration, or noise can be avoided.

Further, by making the calculation cycle T1 an integer multiple of the calculation cycle T2, the number of voltage command value calculation processes with a large calculation load can be reduced while suppressing waveform distortion of the voltage command value.
Further, the duty command value calculation unit calculates ΔVa = ((√3) / 3) × Δθ based on the three-phase voltage command values Va, Vb, Vc calculated for each calculation cycle T1 and the rotation angle Δθ. X (Vc−Vb), ΔVb = ((√3) / 3) × Δθ × (Va−Vc), ΔVc = ((√3) / 3) × Δθ × (Vb−Va) The value deviations ΔVa, ΔVb, ΔVc are calculated every calculation cycle T2. Since the rotation angle θ is not included in the above equation, the sin table reference processing is unnecessary, and the calculation load can be reduced. Even if the calculation cycle T1 is lengthened, a control waveform with less distortion can be generated by performing the duty command value calculation processing with a short calculation cycle T2.

The best mode for carrying out the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic diagram of an electric power steering apparatus according to the present embodiment. This electric power steering apparatus is of a so-called pinion assist type, and the steering 61 is connected to a rack and pinion 66 via a steering shaft 62, universal joints 63 and 64, and a shaft 65. Further, the rack and pinion 66 is provided with a wheel tie rod 67, and the rotational movement of the handle 61 is converted into the axial movement of the tie rod 67.

  A torque sensor 4 is provided on the shaft 65, and the torque sensor 4 can detect a steering torque applied to the steering 61 and output a torque signal. Further, the reduction gear 31 and the motor 3 are attached to the shaft 65, and the rotational torque of the motor 3 is transmitted to the shaft 65 via the reduction gear 31.

  The electric power steering control unit (ECU) 1 calculates the auxiliary steering torque based on the torque signal from the torque sensor 4 and the vehicle speed signal from the vehicle speed sensor 2 as described above, and sends the drive current based on the calculation result to the motor 3. To do. An ON / OFF signal of an ignition key 5a is input to the power steering control device 1, and the ECU 1 is configured to start arithmetic processing for auxiliary steering torque by turning on the ignition key 5a.

  FIG. 2 is a block diagram showing a hardware configuration of the electric power steering control device 1. The electric power steering control device 1 includes an A / D converter 110, an interface 111, a CPU 113, a ROM 114, a RAM 115, a flash ROM 116, a PWM controller 117, a motor drive circuit 119, a motor current detection circuit 120, a bus 121, a reference voltage generation circuit 130, A constant voltage circuit 140 and the like are provided.

  The bus 121 is for transmitting and receiving data among the A / D converter 110, the interface 111, the interrupt controller 112, the CPU 113, the ROM 114, the RAM 115, and the like. The A / D converter 110 inputs the main torque signal and the sub torque signal output from the torque sensor 4, the detection current from the motor current detection circuit 120, and the voltage between the terminals of the motor 3, and converts them into digital signals. is there. The constant voltage circuit 140 is provided to reduce a voltage error after A / D conversion by giving a constant voltage to the A / D converter 110.

  The torque sensor 4 described above includes two output signals of a main torque signal and a sub torque signal, and the total voltage of these signals is set to have a cross characteristic that is a reference voltage (for example, 5 V). That is, when no torque is applied to the steering, the main torque signal and the sub torque signal are each a torque neutral voltage of 2.5 V, and when some torque is applied to the steering, the main torque signal and the sub torque signal are the neutral voltage 2 .5V changes in opposite directions with reference to 5V. The reference voltage generation circuit 130 is for applying the above-mentioned 5V reference voltage to the torque sensor 130.

  The interface 111 counts vehicle speed pulses from the vehicle speed sensor 2 and converts them into digital signals. The ROM 114 is used as a memory for storing a control program for the motor 3, a PWM calculation program, a fail safe program, and the like, and the RAM 115 is used as a work memory for operating the program. The flash ROM 116 can hold the memory contents even after the ignition key 5a is turned off. This flash ROM 109 can store, for example, a control learning result.

  The PWM controller 117 is for converting a signal representing the torque of the motor 3 into pulse command modulated duty command values W, V, U, Wb, Vb, Ub. Here, the pulse signals W, V, and U represent positive-phase three-phase signals, and the pulse signals Wb, Vb, and Ub represent negative-phase three-phase signals.

  The motor drive circuit 119 is composed of an inverter circuit for generating a three-phase current of WVU, and can supply a three-phase current having a predetermined duty ratio to the motor 3 based on a signal given from the PWM controller 117. .

  The motor current detection circuit 120 includes a current-voltage conversion element such as a resistor, and detects a drive current to the motor 3 and outputs a current detection value having a voltage corresponding to the current. The current detection value is amplified by an amplifier circuit (not shown), and then input to the A / D converter 110 and converted into a digital signal. Although not shown, the motor 3 is provided with a resolver for detecting the rotation angle, and the rotation angle signal from the resolver is input to the A / D converter 110. The motor 3 is provided with a temperature sensor (not shown) for detecting the motor temperature, and a temperature signal from the temperature sensor is also input to the A / D converter 110 in the same manner. In this way, it is possible to prevent the motor 3 from being heated by monitoring the signal from the temperature sensor.

  FIG. 3 shows a block diagram of control processing in the electric power steering control device 1. In this figure, a phase compensation unit 301, a basic assist control unit 302, a compensation control unit 303, a current command value calculation unit 304, adders 310a to 310c, PI control units 311a to 311c, a three-phase-dq conversion unit 312, dq- Each function of the three-phase conversion unit 313 and each eye opening detection unit 316 is realized by software processing of the CPU 113. In addition, the phase compensation unit 301, the basic assist control unit 302, the compensation control unit 303, the current command value calculation unit 304, the adders 310a to 310c, the PI control units 311a to 311c, and the three-phase-dq conversion unit 312 are executed at a cycle T1. The dq-3 phase conversion unit 313 and the rotation angle detection unit 316 are executed in the cycle T2. Here, the period T2 is set shorter than T1, and the period T2 is set to 1 / integer of T1. For example, when the duty command value calculation cycle T2 is 25 μsec, the current command value calculation cycle T1 can be set to 4 × T2 = 1 msec.

  The phase compensation unit 301 is for compensating the frequency characteristics of the control system and ensuring the stability of the control by combining the phase delay control and the phase advance control based on the input torque signal. The basic assist control unit 302 sets an independent assist torque map for each vehicle speed and calculates an assist torque according to the vehicle speed in order to achieve steering in the low speed range and handle stability in the high speed range. Yes.

  The compensation control unit 303 is for compensating for the steering feeling caused by the moment of inertia of the motor 3, and can improve the steering feeling in the high speed range based on the differential value of the torque signal and the vehicle speed signal. is there. Further, the compensation control unit 303 can execute a convergence process, an inertia compensation process, and a SAT (self-aligning torque) estimation process. The convergence process is a process for calculating a compensation value for improving the convergence of the control based on the angular velocity of the motor. The inertia compensation process is for improving the steering feeling during high-speed traveling based on the differential value of the torque signal and the vehicle speed signal. In other words, since the motor has a large moment of inertia, the steering feeling during high-speed running has a sense of inertia, and therefore processing for canceling the sense of inertia is performed by inertia compensation processing.

  The compensation control unit 303 can also calculate a self-aligning torque for steering wheel return compensation. In general, in the electric power steering apparatus, the self-aligning torque tends to be weak due to the influence of the reduction gear 31 and the like, and thus the handle 61 is difficult to return to the neutral position. Therefore, by calculating the compensation current value for restoring the steering wheel to the neutral position based on the motor angular velocity, angular acceleration, and torque signal when the motor 3 is rotated by the action of the self-aligning torque, the steering wheel return compensation is performed. It can be carried out.

  The current command value calculation unit 304 calculates a current command value for the motor 3 based on signals from the basic assist control unit 302 and the compensation control unit 303. The current command value is represented by three phases (U, V, W), and each current command value is input to the adders 310a to 310c. The adders 310a to 311c have a function of calculating a difference current value representing a difference between the current command value and the current value detected by the current detection circuits 120a to 120c.

  The PI control units 311a to 311c calculate voltage command values Va, Vb, and Vc by performing control that combines proportional control and integral control based on the calculated differential current value. The three-phase-dq converter 312 has a function of converting the three-phase voltage command values Va, Vb, Vc into the two-phase voltage command values Vd, Vq based on the rotation angle θ. The voltage command value Vd corresponds to the coordinate axis of the field current of the d-axis induction motor, and the voltage command value Vq corresponds to the coordinate axis of the excitation current.

  Further, the dq-3 phase conversion unit 313 converts the voltage command values Vd, Vq into three-phase voltage command values Va ′, Vb ′, Vc ′ again based on the rotation angles θ, Δθ, and these signals. This is for outputting to the PWM controller 117. As a result, a three-phase motor drive current subjected to pulse width modulation is supplied to the motor 3. The resolver 315 is for outputting a signal representing the shaft angle of the motor 3, and the rotation angle detection unit 316 calculates the rotation angle θ and Δθ of the motor based on the input signal, and outputs these signals to 3 It is configured to output to the phase-dq conversion unit 312 and the dq-3 phase conversion unit 313.

Next, an outline of signal processing in the electric power steering control device according to the present embodiment will be described. First, the process of converting the voltage command value into three-phase-dq conversion and dq-3 phase conversion is given by

すなわち、ｄｑ−３相変換部３１３における電圧指令値Ｖａ’，Ｖｂ’，Ｖｃ’は次式のように三角関数を含まない演算式に簡略化できる。

Here, the voltage command values Vd and Vq on the dq axis can be regarded as being constant in a sufficiently short time (for example, the calculation cycle T2). Further, if the motor rotation angle in the duty calculation cycle T2 is set to Δθ = ωT2, the calculation cycle T2 is sufficiently small. Therefore, it can be approximated that cos Δθ≈1, sin Δθ≈Δθ.

That is, the voltage command values Va ′, Vb ′, and Vc ′ in the dq-3 phase conversion unit 313 can be simplified to an arithmetic expression that does not include a trigonometric function as in the following expression.

  Thus, for each duty command value calculation cycle T2, a deviation (√3 / 3) · Δθ (Vc−Vb) is calculated, and a voltage command value with less distortion can be obtained simply by adding this deviation to the voltage command value. Can be generated. An example of the generated waveform is shown in FIG. In this figure, the current control calculation cycle T1 is set to four times the duty command value calculation cycle T2, and it is confirmed that a control voltage waveform with less distortion can be generated by adding the calculated deviation for each cycle T2. it can.

  That is, according to the present embodiment, since the above-described processing can be realized only by adding a deviation, complicated calculations such as reference to a sin table and shift calculation are not required. For this reason, it is possible to generate a control voltage waveform with less distortion while reducing the calculation load on the CPU. Even if the current control calculation cycle T1 with a large calculation load is set to be long, the waveform distortion can be suppressed, and the calculation load can be reduced.

  Next, the operation of the electric power steering control device according to the present embodiment will be described with reference to the flowchart of FIG. First, when the ignition switch 5a is turned on, the CPU 113 performs initial settings such as self-diagnosis processing and timer reset (step S51). Subsequently, the CPU 113 starts a timer (step S52), and determines whether or not the timer has elapsed for the period T1 (step S53). When the timer has elapsed by the period T1 (YES in step S52), the CPU 113 calculates a current command value based on the A / D converted torque signal or the like (step S54) (step S55). Further, the CPU 113 calculates voltage command values Va, Vb, and Vc based on the difference between the current command value and the current detection value (step S56).

Next, when the counter timer has elapsed by the period T2 (YES in step S57), the CPU 113 calculates voltage command value deviations ΔVa, ΔVb, ΔVc based on the voltage command values Va, Vb, Vc calculated in step S56 ( Step S58). The voltage command value deviations ΔVa, ΔVb, ΔVc are calculated according to the following equations.
ΔVa = ((√3) / 3) × Δθ × (Vc−Vb),
ΔVb = ((√3) / 3) × Δθ × (Va−Vc),
ΔVc = ((√3) / 3) × Δθ × (Vb−Va),

  In this equation, it can be calculated that Δθ = ω × T2, and it is understood that the voltage command value deviations ΔVa, ΔVb, and ΔVc can be calculated by simple calculation. Subsequently, the CPU 113 adds the voltage command value deviations ΔVa, ΔVb, ΔVc to the current voltage command values Va, Vb, Vc, and calculates new voltage command values Va ′, Vb ′, Vc ′ (step S59). The PWM controller 117 outputs a three-phase drive current to the motor 3 based on the new voltage command values Va ', Vb', Vc ', so that auxiliary torque is applied to the steering (step S59).

  Similarly, the above-described processing is repeatedly executed until the ignition switch is turned off (YES in step S60). That is, when the counter timer has elapsed for the next period T2 (YES in step S57), the CPU 113 calculates voltage command value deviations ΔVa, ΔVb, ΔVc (step S58), and these voltage command value deviations ΔVa, ΔVb. , ΔVc are added to the previously calculated voltage command values Va ′, Vb ′, Vc ′ (step S59). A duty value is determined based on the voltage command values Va ′, Vb ′, and Vc ′ (step S <b> 60), and a three-phase drive current is supplied to the motor 3 from the PWM controller 117.

When the calculation cycle T1 is set to four times the calculation cycle T2, the duty command value calculation processing (steps S57 to S59) is performed four times for each current command value calculation processing (steps S53 to S56). Repeated. According to the present embodiment, as shown in FIG. 4, even if the current command value calculation cycle T1 is set long, a waveform with the same accuracy as when the current command value calculation processing is executed every cycle T2 is generated. can do.
In the above-described embodiment, the configuration of the three-phase current control is shown, but it goes without saying that the present invention can also be applied to the configuration of the dq-phase current control.

1 is a schematic view of an electric power steering apparatus according to an embodiment of the present invention. 1 is a block diagram of an electric power steering control device according to an embodiment of the present invention. It is a functional block diagram of the electric power steering control device according to the embodiment of the present invention. It is a graph showing an example of the voltage command value concerning the embodiment of the present invention. It is a flowchart showing operation | movement of the electric power steering control apparatus which concerns on embodiment of this invention. It is a flowchart showing operation | movement of the electric power steering control apparatus which concerns on embodiment of this invention. It is a figure for demonstrating the conventional power steering control apparatus.

Explanation of symbols

1 ECU
3 Motor 4 Torque sensor 30 Torque calculation process 31 Motor control process 32 Compensation control process 33 Sensor process 113 CPU

Claims (4)

A current command value calculator for calculating a current command value based on a steering torque applied to the steering;
A voltage command value calculation unit that calculates a voltage command value for each calculation cycle T1, based on the difference between the PWM drive current supplied to the motor for generating steering assist torque and the current command value;
A voltage command value deviation represented by the voltage command value and a rotation angle Δθ of the motor in a calculation cycle T2 shorter than the calculation cycle T1 is calculated, and the voltage command value deviation is calculated for each calculation cycle T2. An electric power steering control device comprising: a duty command value calculation unit that calculates a duty command value of the PWM drive current by accumulating the value.   The electric power steering control device according to claim 1, wherein the calculation cycle T1 is an integral multiple of the calculation cycle T2. The duty command value calculation unit is based on the three-phase voltage command values Va, Vb, Vc and the rotation angle Δθ calculated for each calculation cycle T1, respectively.
ΔVa = ((√3) / 3) × Δθ × (Vc−Vb),
ΔVb = ((√3) / 3) × Δθ × (Va−Vc),
ΔVc = ((√3) / 3) × Δθ × (Vb−Va),
2. The electric power steering control device according to claim 1, wherein the voltage command value deviations ΔVa, ΔVb, and ΔVc expressed by: Calculating a current command value based on a steering torque applied to the steering;
Calculating a voltage command value for each calculation cycle T1, based on the difference between the PWM drive current supplied to the steering assist torque generating motor and the current command value;
A voltage command value deviation represented by the voltage command value and a rotation angle Δθ of the motor in a calculation cycle T2 shorter than the calculation cycle T1 is calculated, and the voltage command value deviation is calculated for each calculation cycle T2. An electric power steering control method comprising: calculating a duty command value of the PWM drive current by accumulating the value.

Images