Motor open-phase detection method based on signal injection and based on two-stage screening and signal injection

Abstract

The application discloses a motor open-phase detection method based on signal injection and two-stage screening and signal injection. Before starting of a motor, single-phase directional injection detection is sequentially performed on U phase, V phase and W phase of the motor without depending on rotor angle information. For each phase, a static voltage vector output by an inverter is controlled to be fixedly directed to an axis of the phase winding, a current response of the phase is detected, and if the current response is lower than a threshold value, it is determined that the phase is open-phase. The application realizes reliable and robust diagnosis of open-phase faults before starting, thereby fundamentally guaranteeing starting safety of a motor driving system.

Description

Technical Field

[0001] This invention relates to the field of motor fault detection technology, and in particular to a motor phase loss detection method based on signal injection and a two-stage screening and signal injection method. Background Technology

[0002] Permanent magnet synchronous motors are widely used in industrial drives, new energy vehicles, and other fields due to their high efficiency and high power density. Their drive system typically consists of a controller, a three-phase inverter bridge, and the motor itself. The power switching transistors (such as IGBTs) in the inverter bridge are the core and weakest link of the system. If the motor is forcibly started with one phase winding open (phase loss), it will cause a severe current imbalance, generating a huge inrush current and torque, which can easily burn out the power switching transistors instantly, causing significant losses.

[0003] Therefore, performing a phase loss self-test on the motor windings before powering on the system is a crucial safety function. Traditional multimeter measurement methods cannot automate this process. The current mainstream solution is the "active signal injection method," which uses the controller itself and the existing inverter bridge to inject a detection signal into the windings when the motor is stationary, and then analyzes the feedback current response to determine the circuit integrity.

[0004] Existing methods for detecting phase loss before motor startup primarily rely on injecting current in the same direction as the rotor (D-axis) when the motor is stationary, and then detecting the three-phase current response to determine if a phase is missing. This method has a fundamental flaw: its detection results are heavily dependent on the accuracy of the rotor position sensor and the initial angle of the motor rotor.

[0005] When the rotor's initial position is such that the D-axis magnetic field is perpendicular to a certain phase winding, the theoretical value of the induced current in that normal phase is zero, and the system will misjudge that phase as missing (false alarm). Similarly, if there is an installation error in the position sensor, it will also cause abnormal current detection in all phases, leading to misjudgments or missed detections, seriously affecting the reliability of the detection. Summary of the Invention

[0006] To address the problems existing in the prior art, the purpose of this invention is to provide a motor phase loss detection method based on signal injection and a two-stage screening and signal injection method. This invention, through innovative two-stage detection logic, especially by introducing a single-phase orientation verification mechanism that does not rely on angle information, can completely eliminate misjudgments and missed judgments caused by "geometric zero point" and sensor errors, and achieve reliable and robust diagnosis of phase loss faults before startup, thereby fundamentally ensuring the startup safety of the motor drive system.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is: a motor phase loss detection method based on signal injection. Before the motor starts, without relying on rotor angle information, single-phase directional injection detection is performed on the U phase, V phase, and W phase of the motor respectively. For each phase, the inverter outputs a stationary voltage vector with a fixed spatial direction pointing to the winding axis of that phase, and the current response of that phase is detected. If the current response is lower than the threshold, the phase is determined to be missing.

[0008] As a further improvement to the present invention, the specific steps include:

[0009] Step 1: Construct a single-phase test voltage vector: Assuming the target phase is phase X, where X is U, V, or W, the three-phase PWM duty cycle command is set as follows: D_x = 0.5 + D_inj, and the duty cycle of the other two phases is 0.5 - D_inj, where D_inj is a preset fixed value.

[0010] Step 2, Injection and Response Detection: Apply the three-phase PWM duty cycle from Step 1 and continue for a preset detection time; during this period, detect the response of the X-phase current; record the maximum absolute value of its response current, Iu_resp_max;

[0011] Step 3, Adaptive threshold decision: Calculate an expected normal current response value I_expected. If Iu_resp_max < I_expected / K, where K is the safety factor, then phase X is determined to be missing; otherwise, the motor is determined to be normal.

[0012] This invention also provides a method for detecting motor phase loss based on two-stage screening and signal injection, comprising:

[0013] The first stage is broad-spectrum screening and suspected fault phase locking: D-axis excitation current is injected into the motor, and the three-phase current is continuously sampled during the injection period. The historical maximum value of the absolute value of each phase current during the injection period is recorded, and one or more phases whose historical maximum value is lower than the first threshold are marked as suspected fault phases.

[0014] The second stage, single-phase directional injection and final confirmation: For the suspected faulty phase, without relying on rotor angle information, the inverter outputs a stationary voltage vector with a fixed spatial direction pointing to the winding axis of the phase, performs single-point directional excitation on the phase, and detects the current response of the phase. If the current response is lower than the second threshold, the phase is confirmed to be missing.

[0015] As a further improvement of the present invention, the injection of D-axis excitation current into the motor in the first stage is specifically as follows:

[0016] Initialize the counter and clear the maximum value record of the three-phase current. Set the D-axis current command to the preset value and the Q-axis current command to zero. Read the current rotor position sensor angle and perform closed-loop control through the FOC current loop. Calculate the three-phase PWM duty cycle command and drive the inverter bridge to output the corresponding PWM waveform to establish a stable stationary magnetic field in the D-axis direction within the motor.

[0017] As a further improvement of the present invention, the first stage further includes an injection maintenance control step, as follows:

[0018] Obtain the maximum value among the current three-phase currents. When the maximum value of the current three-phase current is less than the D-axis current command and the injection duration is less than the preset maximum time, maintain the injection state. When the maximum value of the current three-phase current reaches the D-axis current command or the injection duration reaches the preset maximum time, stop the injection and switch to the suspected fault phase determination.

[0019] As a further improvement of the present invention, in the first stage, the sampled instantaneous values ​​of the three-phase current are subjected to first-order low-pass digital filtering, and then the historical maximum values ​​of the absolute values ​​of each phase current are updated.

[0020] As a further improvement of the present invention, the second stage specifically includes the following steps:

[0021] Step 1: Construct a single-phase test voltage vector: Assuming the suspected faulty phase marked in the first stage is phase X, where X is U, V, or W, the three-phase PWM duty cycle command is set as: D_x = 0.5 + D_inj, and the duty cycle of the other two phases is 0.5 - D_inj, where D_inj is a preset fixed value;

[0022] Step 2, Injection and Response Detection: Apply the three-phase PWM duty cycle from Step 1 and continue for a preset detection time; during this period, detect the response of the X-phase current; record the maximum absolute value of its response current, Iu_resp_max;

[0023] Step 3, Adaptive threshold decision: Calculate an expected normal current response value I_expected. If Iu_resp_max < I_expected / K, where K is the safety factor, then phase X is determined to be missing; otherwise, the motor is determined to be normal.

[0024] As a further improvement of the present invention, after the first stage ends, before the second stage begins, and after the entire detection is completed, a discharge waiting state is entered. In this state, the duty cycle of the three-phase PWM is set to 0.5, that is, the upper and lower transistors of the inverter bridge are each turned on for 50%, which is equivalent to short-circuiting the three-phase windings of the motor, so that the magnetic energy stored in the windings is quickly released through the freewheeling diodes; the state is switched only after the detection that the three-phase current has decayed to below the safe value.

[0025] The beneficial effects of this invention are:

[0026] This invention, through its core design of "two-stage verification" and "single-phase physical direct measurement," fundamentally solves the problem of the absolute dependence on angle information in existing technologies, specifically manifested in:

[0027] 1. False Alarm Resolution: The first stage employs a "peak recording" strategy, ensuring that even if the rotor stops at a specific angle that momentarily reduces the current in a certain phase to zero, the maximum current value of that normal phase will still significantly exceed zero due to system dynamics during continuous closed-loop injection, thus avoiding false alarms. This filters out most false fault signals caused by "geometric zero points."

[0028] 2. Eliminating Angle Dependence: The second stage completely abandons the use of rotor angle information and directly applies a directional voltage to the suspected phase. Regardless of the rotor's position, this test voltage forces current to flow into the tested phase. If the winding circuit is normal, a detectable current will be generated; if the circuit is open, there will be no current. This method fundamentally eliminates the possibility of misjudgment due to rotor position or sensor error, achieving 100% reliable diagnosis.

[0029] 3. Ensuring Safety and Compatibility: The small signal injection and active discharge mechanism ensures that the detection process is torque-free, shock-free, and energy-free, guaranteeing the safety of the detection itself and enabling seamless switching with normal operating modes. Furthermore, the method relies solely on the standard hardware of existing drive systems (MCU, inverter bridge, current sampling), requiring no additional cost.

[0030] Therefore, this invention combines the advantages of high reliability (eliminating false alarms and ensuring detection), strong robustness (insensitive to sensor errors) and high practicality (fully software-implemented, safe and seamless). Attached Figure Description

[0031] Figure 1 This is an overall flowchart of Embodiment 1 of the present invention;

[0032] Figure 2 This is a flowchart of the first stage state in Embodiment 1 of the present invention;

[0033] Figure 3 This is a flowchart of the second stage state in Embodiment 1 of the present invention. Detailed Implementation

[0034] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0035] Example 1

[0036] Explanation of related terms

[0037] D-axis / Q-axis: A rotating coordinate system defined in motor vector control. The D-axis (direct axis) is aligned with the direction of the rotor's permanent magnet magnetic field, while the Q-axis (quadrature axis) leads the D-axis by 90 electrical degrees. When only D-axis current is injected, it primarily generates the excitation magnetic field and does not produce the torque that causes the motor to rotate.

[0038] Rotary transformer: A sensor used to measure the absolute position and speed of an electric motor rotor.

[0039] Phase loss: A state in which one or more phases of the three-phase winding of a motor are open-circuited or have poor contact, resulting in the inability of current to flow normally.

[0040] PWM: Pulse Width Modulation. A technique that controls the average output voltage by adjusting the on-time ratio (duty cycle) of a switching transistor within one cycle.

[0041] FOC: Field-Oriented Control. A high-performance algorithm that simulates an AC motor as a DC motor for control through coordinate transformation.

[0042] First-order low-pass filter: A filter that allows low-frequency signals to pass through while suppressing high-frequency signals. It is used to smooth sampled current signals and filter out switching noise. Its discretization formula can be expressed as: y(n) = α * x(n) + (1-α) * y(n-1), where x(n) is the current input, y(n) is the current output, and α is the filter coefficient.

[0043] Suspected faulty phase: In the first stage of detection, the phase with the maximum current response below the threshold is marked as an object to be further confirmed.

[0044] like Figure 1 As shown, a method for detecting motor phase loss based on two-stage screening and signal injection includes:

[0045] Phase 1 (Broad-spectrum Screening): While the motor is stationary, D-axis excitation current is injected. Unlike traditional methods that compare instantaneous values, this invention records the maximum absolute value of each of the three-phase currents throughout the injection period. By comparing these historical maximum values ​​with thresholds, "suspected fault phases" with abnormally weak responses are identified. This "peak recording" strategy effectively avoids misjudgments of instantaneous zero current caused by the rotor stopping at a specific angle.

[0046] The second stage (directional confirmation): For the "suspected faulty phase", the reliance on rotor angle information is completely abandoned. Instead, a static voltage vector with a fixed spatial direction pointing towards the winding of that phase is directly controlled by the inverter for "single-point testing". If the phase still cannot generate sufficient current under this directional excitation, it is confirmed as a physical phase loss fault.

[0047] The two stages of this embodiment will be further explained below:

[0048] like Figure 2 As shown, the first stage: broad-spectrum screening and identification of suspected faults:

[0049] The purpose of this stage is to quickly and initially identify abnormally weak phases in the current response, while avoiding momentary misjudgments caused by special rotor angles through a "record maximum value" strategy, and to safely terminate the process under controlled conditions; specifically including:

[0050] Step 1: D-axis excitation injection:

[0051] The system is powered on, and the motor is stationary. The counters are initialized to openphase_counter = 0, and the maximum three-phase current records Iu_max, Iv_max, Iw_max are cleared to 0.

[0052] The controller sets the D-axis current command Id_ref = I_set (e.g., 20A) and the Q-axis current command Iq_ref = 0.

[0053] The current rotor position sensor angle θ is read, and closed-loop control is performed through the FOC current loop (including Park inverse transformation, SVPWM modulation, etc.). The three-phase PWM duty cycle command is calculated, and the inverter bridge is driven to output the corresponding PWM waveform to establish a stable stationary magnetic field in the D-axis direction within the motor.

[0054] Step 2: Injection maintenance condition assessment and safe exit:

[0055] In each control cycle (e.g., in the PWM interrupt service routine), the following decision logic is executed:

[0056] Condition A (Current loop tracking complete): Obtain the maximum value i_current_max among the current three-phase currents (take the maximum from |Iu|, |Iv|, |Iw|).

[0057] Condition B (Longest Injection Time): Check if the counter openphase_counter is less than the preset maximum count value CNT_MAX (e.g., 3000, representing an injection time of approximately 300ms).

[0058] Logical condition: The system maintains D-axis current injection only when both conditions are met: i_current_max < Id_ref and openphase_counter < CNT_MAX. This ensures that current commands can be tracked and that injection is not unlimited.

[0059] Exit Mechanism: If any of the above conditions are not met (i.e., the current has reached the command value, or the injection time has expired), the three-phase PWM duty cycle command is immediately set to 0.5 (or all IGBTs are turned off and enter a high-impedance state), forcibly stopping energy injection and proceeding to step four for result judgment. This design ensures that the injection process is controlled and safe.

[0060] Step 3: Signal Processing and Peak Capture

[0061] Within each control cycle that meets the above maintenance conditions:

[0062] Current sampling and filtering: The three-phase currents Iu, Iv, and Iw are sampled in real time at the control frequency. To suppress switching noise, the instantaneous value of each phase current is subjected to a first-order low-pass digital filter to obtain smoothed current values ​​Iu_f, Iv_f, and Iw_f.

[0063] Peak Capture and Recording: Updates the historical maximum value of the absolute value of the three-phase current, as detailed below:

[0064] Iu_max = max(Iu_max, |Iu_f|);

[0065] Iv_max = max(Iv_max, |Iv_f|);

[0066] Iw_max = max(Iw_max, |Iw_f|);

[0067] Increment the counter: openphase_counter = openphase_counter + 1.

[0068] Technical principle: During the injection period, the system continuously monitors the absolute value of the three-phase filtered current. Traditional methods only compare instantaneous values, which are easily affected by the initial rotor position (for example, when the D-axis is perpendicular to a certain phase winding, the theoretical value of the current in that phase is 0). The current of a missing phase may not be the minimum value among the current three-phase currents. Therefore, the method of judging the minimum value of the instantaneous three-phase current as a suspected phase loss is not advisable.

[0069] Using the historical maximum value of the three-phase current as the criterion ensures that even if the rotor's initial position causes the current of a certain phase to be zero at the moment of injection, during the closed-loop control process of several hundred milliseconds, due to minute digital quantization errors, sensor noise, or slight magnetic circuit saturation effects, the current of that normal phase will deviate from the theoretical zero point, and its absolute value will show a peak value significantly greater than zero. Recording this peak value, rather than the instantaneous value at a certain moment, is the key to avoiding the misjudgment of the "geometric zero point".

[0070] Step 4: Identification of suspected fault phases:

[0071] When the detection exits due to the achievement of current or time conditions, the recorded three-phase peak values ​​Iu_max, Iv_max, Iw_max are compared with a lower absolute threshold I_th_low (e.g., 2.0A).

[0072] Judgment logic: If the historical maximum value of a certain phase is less than the threshold Ix_max < I_th_low, then the phase is marked as a "suspected fault phase".

[0073] If the peak values ​​of all three phases are greater than I_th_low, the motor is determined to be normal in all three phases. The entire detection process ends directly, and the motor enters the "discharge waiting state". After the magnetic energy stored in the windings is released, the motor enters the normal operation state.

[0074] If at least one phase is marked as a suspected faulty phase, the system also enters a "discharge waiting state" until the magnetic energy stored in the winding is released before proceeding to the second stage for final confirmation.

[0075] like Figure 3 As shown, the second stage, single-phase directional injection, and final confirmation:

[0076] The purpose of this stage is to confirm the diagnosis of "suspected faulty phases." Its key innovation lies in completely bypassing rotor position sensors and FOC coordinate transformation, directly performing "energization testing" on specific phases; specifically including:

[0077] Step 1: Construct a single-phase test voltage vector:

[0078] Assume the suspected faulty phase identified in the first stage is phase U. Instead of using angle θ, the controller directly constructs a voltage vector flowing from phase U to phases V and W in a stationary coordinate system by adjusting the duty cycle of the three-phase PWM. One specific implementation is as follows:

[0079] Du = 0.5 + D_inj;

[0080] Dv = 0.5 - D_inj;

[0081] Dw = 0.5 - D_inj;

[0082] Where Du, Dv, and Dw are the PWM duty cycle commands (0~1) for the U, V, and W phases, respectively, and D_inj is a preset fixed constant with a small amplitude (e.g., 0.05), where 0.5 represents the zero-voltage reference at the midpoint of the inverter bridge. This voltage combination spatially synthesizes a stationary voltage vector with a fixed amplitude and a direction strictly pointing towards the axis of the U-phase winding.

[0083] Step 2, Injection and Response Detection:

[0084] Apply the aforementioned duty cycle for a short detection time. During this time, detect the response of the U-phase current. Also record the maximum absolute value of the response current, Iu_resp_max.

[0085] Step 3: Adaptive threshold decision:

[0086] A relative threshold method is used for the final judgment to improve adaptability to different motors and bus voltages. An expected normal current response value I_expected is calculated (which can be estimated based on bus voltage, D_inj, and motor phase resistance).

[0087] The decision logic is as follows: if Iu_resp_max < I_expected / K (where K is a safety factor, such as 4), then the U phase is confirmed to be missing, the system reports an error and prohibits startup. Otherwise, the motor is considered to be normal.

[0088] Safety state machine and discharge process: The entire detection process is managed by a well-defined state machine, which includes states such as "idle", "first stage injection", "discharge waiting", "second stage injection", "fault", and "normal".

[0089] Discharge Waiting State: The system enters this state after the first stage ends and before the second stage begins, and at the end of the entire detection process. In this state, the controller sets the duty cycle of all three phases of the PWM to 0.5 (i.e., the upper and lower transistors of the inverter bridge are each conducting for 50%, equivalent to short-circuiting the three-phase windings of the motor), allowing the magnetic energy stored in the windings to be quickly released through the freewheeling diodes. Switching to the next state is only permitted when all three phase currents have decayed to near zero (e.g., less than 0.1A). This ensures no current superposition interference between stages and that the motor has no residual current after the detection ends, allowing for a safe transition to the operating mode.

[0090] Example 2

[0091] This embodiment is a simplification and variation of the "two-stage" method in Embodiment 1. The first stage is completely omitted; before startup, without relying on any angle information, the aforementioned "single-phase directional injection detection" is directly performed sequentially on the U, V, and W phases. The specific process is as follows:

[0092] 1. For phase U: Apply D_u=0.5+D, D_v=0.5-D, D_w=0.5-D, and detect the current response of phase U.

[0093] 2. After discharge, apply D_v=0.5+D, D_u=0.5-D, D_w=0.5-D to phase V and detect the current response of phase V.

[0094] 3. After discharge, apply D_w=0.5+D, D_u=0.5-D, D_v=0.5-D to phase W and detect the phase W current.

[0095] The advantage of this embodiment is that the logic is simpler, and it completely and thoroughly eliminates reliance on rotor position sensors while still achieving reliable phase loss detection. The disadvantages are that the detection time is slightly longer (requiring three executions), and frequent vector switching may cause slight rotor vibration.

[0096] The embodiments described above are merely illustrative of specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for detecting phase loss in a motor based on signal injection, characterized in that, Before the motor starts, without relying on rotor angle information, single-phase directional injection detection is performed on the U-phase, V-phase, and W-phase of the motor in sequence: for each phase, the inverter output static voltage vector is fixedly pointed to the axis of the winding of that phase, and the current response of that phase is detected. If the current response is lower than the threshold, it is determined that the phase is missing.

2. The method for detecting phase loss in a motor based on signal injection according to claim 1, characterized in that, Specifically, the following steps are included: Step 1: Construct a single-phase test voltage vector: Assuming the target phase is phase X, where X is U, V, or W, the three-phase PWM duty cycle command is set as follows: D_x = 0.5 + D_inj, and the duty cycle of the other two phases is 0.5 - D_inj, where D_inj is a preset fixed value. Step 2, Injection and Response Detection: Apply the three-phase PWM duty cycle from Step 1 and continue for a preset detection time; during this period, detect the response of the X-phase current; record the maximum absolute value of its response current, Iu_resp_max; Step 3, Adaptive threshold decision: Calculate an expected normal current response value I_expected. If Iu_resp_max < I_expected / K, where K is the safety factor, then phase X is determined to be missing; otherwise, the motor is determined to be normal.

3. A method for detecting motor phase loss based on two-stage screening and signal injection, characterized in that, include: The first stage is broad-spectrum screening and suspected fault phase locking: D-axis excitation current is injected into the motor, and the three-phase current is continuously sampled during the injection period. The historical maximum value of the absolute value of each phase current during the injection period is recorded, and one or more phases whose historical maximum value is lower than the first threshold are marked as suspected fault phases. The second stage, single-phase directional injection and final confirmation: For the suspected faulty phase, without relying on rotor angle information, the inverter outputs a stationary voltage vector with a fixed spatial direction pointing to the winding axis of the phase, performs single-point directional excitation on the phase, and detects the current response of the phase. If the current response is lower than the second threshold, the phase is confirmed to be missing.

4. The motor phase loss detection method based on two-stage screening and signal injection according to claim 3, characterized in that, In the first stage, the D-axis excitation current injected into the motor is as follows: Initialize the counter and clear the maximum value record of the three-phase current. Set the D-axis current command to the preset value and the Q-axis current command to zero. Read the current rotor position sensor angle and perform closed-loop control through the FOC current loop. Calculate the three-phase PWM duty cycle command and drive the inverter bridge to output the corresponding PWM waveform to establish a stable stationary magnetic field in the D-axis direction within the motor.

5. The motor phase loss detection method based on two-stage screening and signal injection according to claim 4, characterized in that, The first stage also includes an injection maintenance control step, as detailed below: Obtain the maximum value of the current three-phase current, and maintain the injection state when the current maximum value of the three-phase current is less than the D-axis current command and the injection duration is less than the preset maximum time. When the current maximum value of the three-phase current reaches the D-axis current command or the injection duration reaches the preset maximum time, the injection stops and the process switches to suspected fault phase determination.

6. The motor phase loss detection method based on two-stage screening and signal injection according to claim 3, characterized in that, In the first stage, the sampled instantaneous values ​​of the three-phase current are subjected to a first-order low-pass digital filter, and then the historical maximum values ​​of the absolute values ​​of each phase current are updated.

7. The motor phase loss detection method based on two-stage screening and signal injection according to claim 3, characterized in that, The second stage specifically includes the following steps: Step 1: Construct a single-phase test voltage vector: Assuming the suspected faulty phase marked in the first stage is phase X, where X is U, V, or W, the three-phase PWM duty cycle command is set as: D_x = 0.5 + D_inj, and the duty cycle of the other two phases is 0.5 - D_inj, where D_inj is a preset fixed value; Step 2, Injection and Response Detection: Apply the three-phase PWM duty cycle from Step 1 and continue for a preset detection time; during this period, detect the response of the X-phase current; record the maximum absolute value of its response current, Iu_resp_max; Step 3, Adaptive threshold decision: Calculate an expected normal current response value I_expected. If Iu_resp_max < I_expected / K, where K is the safety factor, then phase X is determined to be missing; otherwise, the motor is determined to be normal.

8. The motor phase loss detection method based on two-stage screening and signal injection according to any one of claims 3-7, characterized in that, After the first stage ends, before the second stage begins, and after the entire detection is completed, the system enters a discharge waiting state. In this state, the duty cycle of the three-phase PWM is set to 0.5, that is, the upper and lower transistors of the inverter bridge are each turned on for 50%, which is equivalent to short-circuiting the three-phase windings of the motor, so that the magnetic energy stored in the windings is quickly released through the freewheeling diodes. The state is switched only after the three-phase current is detected to have decayed to below the safe value.

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