A broken-phase diagnosis method based on current instruction reconstruction and negative-sequence current extraction

Abstract

The present invention relates to the technical field of EPS motors, and specifically to a phase break diagnosis method based on current command reconstruction and negative sequence current extraction. Compared with the prior art, the present invention designs a phase break diagnosis method based on current command reconstruction and negative sequence current extraction, and determines whether a phase break fault has occurred by the difference between the reference negative sequence component and the negative sequence component of the U-phase current. Under various operating conditions of the EPS motor, the phase break fault occurring in the motor phase separation MOSFET can be quickly and accurately diagnosed, enabling the system to enter a safe state.

Description

Technical Field

[0001] The present invention relates to the technical field of EPS motors, and specifically to a phase break diagnosis method based on current command reconstruction and negative sequence current extraction. Background Art

[0002] Currently, the automotive industry is developing rapidly, the degree of automotive electrification is getting higher and higher, and consumers have higher and higher requirements for the driving experience of automobiles. The Electric Power Steering System (EPS) is a power steering system that directly relies on an electric motor to provide auxiliary torque, and its safety requirements are very high. Therefore, once a fault occurs in the electric power steering system, it needs to be detected in time and switched to the safe mode.

[0003] Currently, the single-phase phase break diagnosis of most motor drive products is completed through power-on self-check. However, when a phase break occurs during the operation of the motor, it cannot be diagnosed and recognized, and corresponding safety measures cannot be taken, which brings great safety risks to the users of the products. For example, the three-phase two-level drive topology diagram of the EPS motor is as Figure 1 shown. When the power device 1 in the drive circuit is open-circuited, it can be detected by the drive chip. However, when the phase-separated MOSFET 7 is open-circuited, such as when the point a or b is disconnected, it cannot be detected and recognized.

[0004] Therefore, it is necessary to design a phase break diagnosis method based on current command reconstruction and negative sequence current extraction to detect and recognize the open circuit of the phase-separated MOSFET. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a phase break diagnosis method based on current command reconstruction and negative sequence current extraction to detect and recognize the open circuit of the phase-separated MOSFET.

[0006] To achieve the above purpose, the present invention provides a phase break diagnosis method based on current command reconstruction and negative sequence current extraction, including the following steps: Step 1, calculate the d-axis current command value i dref and the q-axis current command value i qref of the motor according to the current torque, speed, and voltage of the motor; Step 2, obtain the U-phase current reference value i dref , the V-phase current reference value i qref , and the W-phase current reference value i uref through the inverse Clark transformation and the inverse Park transformation of the d-axis current command value i vref and the q-axis current command value i wref of the motor; Step 3, calculate the reference negative sequence component i uref of the U-phase current according to the U-phase current reference value i vref , the V-phase current reference value i wref of the V-phase current, and the W-phase current reference value iurefNagtive ; Step 4, calculate the negative sequence component i of the U phase current according to the three-phase current uNagtive ; Step 5, according to the reference negative sequence component i of the U phase current urefNagtive The negative sequence component i of the U phase current uNagtive The difference between the two values ​​determines whether a phase failure has occurred. urefNagtive -i uNagtive ≥Current adjustment value i threshold , then the fault counter increases by one, such as i uNagtive -i uNagtive <Current adjustment value i threshold , then the fault counter is reduced by one; step 6, if the fault counter ≥ N, then set N and trigger a phase failure fault, if the fault counter < N, proceed to step 7; step 7, if the fault counter < 0, then set 0 and return to step 1, if the fault counter ≥ 0, then directly return to step 1.

[0007] In step 1, the motor's d-axis current command value i is calculated. dref , q-axis current command value i qref The formulas are: Among them, T e is the electromagnetic torque, p n is the number of motor pole pairs, ψ f is the permanent magnet flux, L d is the motor d-axis inductance, L q is the motor q-axis inductance, i d is the motor d-axis current, R s is the motor stator resistance, w e is the current speed of the motor, i q is the motor q-axis current, u lim The available voltage limit.

[0008] The U phase current reference value i uref , V phase current reference value i vref ,W phase current reference value i wref The formula is i uref =i dref cosθ-i qref sinθ, Where θ is the rotation angle of the dq coordinate system.

[0009] The reference negative sequence component i of the calculation of the U-phase current is urefNagtive The formula is x bref =i vref (t)-i vref(t - Δt)cos(ωΔt)·cos(ωΔt) - i vref (t - Δt)sinωΔt, x cref =i wref (t) - i wref (t - Δt)cos(ωΔt)·cot(ωΔt) - i wref (t - Δt)sinωΔt, where i vref (t) is the reference value of the V - phase current at time t, i wref (t) is the reference value of the W - phase current at time t, i vref (t - Δt) is the reference value of the V - phase current at time t - Δt, i wref (t - Δt) is the reference value of the W - phase current at time t - Δt, and ωΔt is the current phase difference.

[0010] The formula for calculating the negative - sequence component i uNagtive of the U - phase current is x b =i v (t) - i v (t - Δt)cosωΔtcos(ωΔt) - i v (t - Δ)sinωΔt, x c =i w (t) - i w (t - Δt)cotωΔtcos(ωΔt) - i w (t - Δt)sinωΔt, where i u is the feedback value of the U - phase current, i v is the feedback value of the V - phase current, i w is the feedback value of the W - phase current, i v (t) is the feedback value of the V - phase current at time t, i w (t) is the feedback value of the W - phase current at time t, i v (t - Δt) is the feedback value of the V - phase current at time t - Δt, i w (t - Δt) is the feedback value of the W - phase current at time t - Δt.

[0011] The current calibration value i threshold is calibrated according to the current sampling level of the actual product.

[0012] The said N is determined according to the fault - tolerance time of functional safety and the operation period of the diagnosis strategy.

[0013] Compared with the prior art, the present invention designs a broken-phase diagnosis method based on current command reconstruction and negative-sequence current extraction. Whether a broken-phase fault occurs is judged by the difference between the reference negative-sequence component and the negative-sequence component of the U-phase current. Under various working conditions of the EPS motor, the broken-phase fault of the motor-phase-separated MOSFET can be quickly and accurately diagnosed, enabling the system to enter a safe state. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 FIG. is a three-phase two-level motor drive topology diagram in the prior art.

[0015] Figure 2 FIG. is a flowchart of the broken-phase diagnosis method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be further described below in conjunction with the accompanying drawings.

[0017] Refer to Figure 2 , the present invention provides a broken-phase diagnosis method based on current command reconstruction and negative-sequence current extraction, including the following steps:

[0018] Step 1, calculate the d-axis current command value i dref and q-axis current command value i qref of the motor according to the current torque, speed, and voltage of the motor.

[0019] The formulas for calculating the d-axis current command value i dref and q-axis current command value i qref of the motor are both:

[0020] Among them, T e is the electromagnetic torque, p n is the number of pole pairs of the motor, ψ f is the permanent magnet flux linkage, L d is the d-axis inductance of the motor, L q is the q-axis inductance of the motor, i d is the d-axis current of the motor, R s is the stator resistance of the motor, w e is the current speed of the motor, i q is the q-axis current of the motor, u lim is the available voltage limit value.

[0021] Step 2, through the inverse Clark transformation and inverse Park transformation of the d-axis current command value i dref and q-axis current command value i qref of the motor, obtain the U-phase current reference value i uref and V-phase current reference value i vref, The reference value of the W-phase current is \(i_{W}\) wref .

[0022] , The reference value of the U-phase current is \(i_{U}\) uref , The reference value of the V-phase current is \(i_{V}\) vref , The reference value of the W-phase current is \(i_{W}\) wref The formula is \(i_{U}\) uref = \(i_{U}\) dref \(\cos\theta - i_{V}\) qref \(\sin\theta\), where \(\theta\) is the rotation angle of the d-q coordinate system.

[0023] Step 3, Calculate the negative-sequence component \(i_{U}^{-}\) of the U-phase current according to the reference value of the U-phase current \(i_{U}\) uref , The reference value of the V-phase current \(i_{V}\) vref , The reference value of the W-phase current \(i_{W}\) wref Calculate the negative-sequence component \(i_{U}^{-}\) of the U-phase current urefNagtive .

[0024] The formula for calculating the negative-sequence component \(i_{U}^{-}\) of the U-phase current is \(x_{1}\) urefNagtive = \(i_{V}\) bref \((t)-i_{W}\) vref \((t-\Delta t)\cos(\omega\Delta t)\cdot\cot(\omega\Delta t)-i_{W}\) vref \((t-\Delta t)\sin\omega\Delta t\), \(x_{1}\) vref = \(i_{V}\) cref \((t)-i_{W}\) wref \((t-\Delta t)\cos(\omega\Delta t)\cdot\cot(\omega\Delta t)-i_{W}\) wref \((t-\Delta t)\sin\omega\Delta t\), wref where \(i_{V}\) \((t)\) is the reference value of the V-phase current at time \(t\), \(i_{W}\) vref \((t)\) is the reference value of the W-phase current at time \(t\), \(i_{V}\) wref \((t)\) is the reference value of the W-phase current at time \(t\), \(i_{W}\) vref \((t-\Delta t)\) is the reference value of the V-phase current at time \(t-\Delta t\), \(i_{W}\) wref \((t-\Delta t)\) is the reference value of the W-phase current at time \(t-\Delta t\), \(\omega\Delta t\) is the current phase difference.

[0025] Step 4, Calculate the negative-sequence component \(i_{U}^{-}\) of the U-phase current according to the three-phase current uNagtive .

[0026] The formula for calculating the negative-sequence component \(i_{U}^{-}\) of the U-phase current is \(x_{2}\) uNagtive = \(i_{U}\) b \((t)-i_{V}\) v \((t-\Delta t)\cos\omega\Delta t\cos(\omega\Delta t)-i_{W}\) v \((t-\Delta)\sin\omega\Delta t\), \(x_{2}\) v = \(i_{U}\) c \((t)-i_{V}\) w(t)-i w (t - Δt)cotωΔtcos(ωΔt)-i w (t - Δt)sinωΔt, where i u is the U - phase current feedback value, i v is the V - phase current feedback value, i w is the W - phase current feedback value, i v (t) is the V - phase current feedback value at time t, i w (t) is the W - phase current feedback value at time t, i v (t - Δt) is the V - phase current feedback value at time t - Δt, i w (t - Δt) is the W - phase current feedback value at time t - Δt.

[0027] Step 5, according to the reference negative - sequence component i urefNagtive of the U - phase current and the negative - sequence component i uNagtive of the U - phase current, judge whether a phase - break fault has occurred. If i urefNagtive - i uNagtive ≥ the current calibration value i threshold , the fault counter is incremented by one. If i urefNagtive - i uNagtive < the current calibration value i threshold , the fault counter is decremented by one. The current calibration value i threshold is calibrated according to the current sampling level of the actual product.

[0028] Step 6, if the fault counter ≥ N, set N and trigger a phase - break fault. If the fault counter < N, go to Step 7. N is determined according to the fault - tolerance time of functional safety and the operation period of the diagnostic strategy.

[0029] Step 7, if the fault counter < 0, set it to 0 and return to Step 1. If the fault counter ≥ 0, directly return to Step 1.

Claims

1. A broken-phase diagnosis method based on current command reconstruction and negative-sequence current extraction, characterized in that: It includes the following steps: Step 1, calculate the d-axis current command value i of the motor according to the current torque, speed, and voltage of the motor dref and the q-axis current command value i qref ; Step 2, through the inverse Clark transformation and inverse Park transformation of the d-axis current command value i of the motor dref and the q-axis current command value i qref , obtain the U-phase current reference value i uref , the V-phase current reference value i vref , and the W-phase current reference value i wref ; Step 3, calculate the reference negative-sequence component i of the U-phase current according to the U-phase current reference value i uref , the V-phase current reference value i vref , and the W-phase current reference value i wref urefNagtive ; Step 4, calculate the negative sequence component \(i\) of the U-phase current according to the three-phase current uNagtive ; Step 5, judge whether a phase break fault has occurred according to the difference between the reference negative sequence component \(i\) of the U-phase current urefNagtive and the negative sequence component \(i\) of the U-phase current uNagtive . If \(i\) urefNagtive - \(i\) uNagtive ≥ the current calibration value \(i\) threshold , the fault counter is incremented by one. If \(i\) urefNagtive - \(i\) uNagtive < the current calibration value \(i\) threshold , the fault counter is decremented by one; Step 6, if the fault counter ≥ N, set N and trigger a phase break fault. If the fault counter < N, go to Step 7; Step 7, if the fault counter < 0, set 0 and return to Step 1. If the fault counter ≥ 0, directly return to Step 1.

2. The broken-phase diagnosis method based on current command reconstruction and negative-sequence current extraction according to claim 1, characterized in that: In the above-mentioned step 1, the formula for calculating the d-axis current command value i dref and the q-axis current command value i qref is both: Among them, T e is the electromagnetic torque, p n is the number of pole pairs of the motor, ψ f is the permanent magnet flux linkage, L d is the d-axis inductance of the motor, L q is the q-axis inductance of the motor, i d is the d-axis current of the motor, R s is the stator resistance of the motor, w e is the current rotational speed of the motor, i q is the q-axis current of the motor, u lim is the available voltage limit value.

3. The broken-phase diagnosis method based on current command reconstruction and negative-sequence current extraction according to claim 1, characterized in that: The U-phase current reference value i ured , the V-phase current reference value i vref , and the W-phase current reference value i wref are calculated by the formula i uref = i dref cosθ - i qref sinθ, where θ is the rotation angle of the d-q coordinate system.

4. The broken-phase diagnosis method based on current command reconstruction and negative-sequence current extraction according to claim 1, characterized in that: The formula for calculating the reference negative-sequence component i urefNagtive of the U-phase current is x bref =i vref (t) - i vref (t - Δt)cos(ωΔt)·cot(ωΔt) - i vref (t - Δt)sinωΔt, x cref =i wref (t) - i wref (t - Δt)cos(ωΔt)·cot(ωΔt) - i wref (t - Δt)sinωΔt, where, i vref (t) is the reference value of the V-phase current at time t, i wref (t) is the reference value of the W-phase current at time t, i vref (t - Δt) is the reference value of the V-phase current at time t - Δt, t wref (t - Δt) is the reference value of the W-phase current at time t - Δt, and ωΔt is the current phase difference.

5. The broken-phase diagnosis method based on current command reconstruction and negative-sequence current extraction according to claim 1, characterized in that: The formula for calculating the negative-sequence component i uNagtive of the U-phase current is x b = i v (T) - i v (t - Δt) cot ωΔt cos(ωΔt) - i v (t - Δt) sin ωΔt, x c = i w (t) - i w (t - Δt) cot ωΔt cos(ωΔt) - i w (t - Δt) sin ωΔt, Among them, i u is the U-phase current feedback value, i v is the V-phase current feedback value, i w is the W-phase current feedback value, i v (t) is the V-phase current feedback value at time t, i w (t) is the W-phase current feedback value at time t, i v (t - Δt) is the V-phase current feedback value at time t - Δt, i w (t - Δt) is the W-phase current feedback value at time t - Δt, and ωΔt is the current phase difference.

6. The broken-phase diagnosis method based on current command reconstruction and negative-sequence current extraction according to claim 1, characterized in that: The described current calibration value i threshold is calibrated according to the current sampling level of the actual product.

7. The broken-phase diagnosis method based on current command reconstruction and negative-sequence current extraction according to claim 1, characterized in that: The said N is determined according to the fault tolerance time of functional safety and the operation period of the diagnosis strategy.

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