Method and device for estimating the single-phase resistance of an electric motor

Abstract

The invention relates to a method of estimating a single-phase resistance of a motor by means of an adjustable speed drive (ASD) while the motor is running and / or at standstill, controlled by the adjustable speed drive. The motor is an asynchronous motor or a synchronous motor. The invention also relates to an adjustable speed drive for performing the corresponding method.

Description

Technical Field

[0001] This invention relates to a method for estimating the single-phase resistance of a motor controlled by an adjustable speed drive (ASD) while the motor is running and / or stopped. The motor is either an asynchronous motor or a synchronous motor. The invention also relates to an adjustable speed drive for performing the corresponding method. Background Technology

[0002] According to the current state of the art, various methods are known for online identification of motor resistance. Most known methods involve injecting current into the motor, measuring the effect of this injection, and estimating the resistance of a symmetrical motor based on the measured effect. The term "online identification" can currently refer to the identification of motor resistance while the motor is mounted to a device and can provide driving force to said device. Alternatively or additionally, the term "online identification" can refer to the remote identification of motor resistance via, for example, the Internet or some other remote connection.

[0003] A major problem associated with known methods for identifying motor resistance is that the classic symmetrical detection of motor resistance cannot identify single-phase resistance, but only the equivalent average value.

[0004] To overcome this problem, the present invention provides a method for measuring the resistance of an asymmetrical motor as described in claim 1. Advantageous embodiments of the invention are described in the dependent claims. The invention also relates to an adjustable speed driver for controlling a motor, said adjustable speed driver being adapted to perform the corresponding method. Summary of the Invention

[0005] According to the present invention, a method is provided for estimating the single-phase resistance of a motor controlled by an adjustable speed drive (ASD) when the motor is running and / or stopped.

[0006] The motor can be an asynchronous motor or a synchronous motor. The method includes the following steps:

[0007] • Inject at least two DC currents into the motor as ASD outputs.

[0008] • Determine the output voltage and current generated by the injected DC current.

[0009] • Extract the DC component present in the determined output voltage and current, and

[0010] • Calculate the cumulative output resistance Rs seen by ASD on each phase of the motor.

[0011] The proposed idea improves the main functionality of adjustable speed drives used to control motors. By understanding the imbalance in the output resistance, the control and stability of the drive are improved, especially for high-performance applications where torque and speed performance are critical.

[0012] Extracting the DC component from the determined output voltage and current (i.e., DC voltage and DC current) allows for the determination of the DC stator resistance seen by the ASD (which combines the resistance of the wiring cables and the motor).

[0013] DC current injection can occur at least twice and at different phase angles (e.g., at 0° and 120°). The injection can occur at different times and / or can be aligned with different phases of the motor to serve as an ASD output. The method can be used during motor stop or while the motor is running. Typically, multiple DC current injections can be performed at two or more different phase angles. This allows for the collection of sufficient data to address the identification of resistance on each phase separately.

[0014] Based on the understanding of the resistance Rs at each phase of the motor and thus the asymmetric resistance of the motor, new features and embodiments can be deployed within the context of this invention, some examples of which will be described in the following paragraphs.

[0015] In a preferred embodiment of the invention, the determined output voltage and / or current is measured or estimated.

[0016] In another preferred embodiment of the invention, the injected DC current is synchronized with a different phase angle of the basic output current of the ASD.

[0017] The phase angles can be different and can vary. The single-phase resistance (or asymmetrical resistance) as seen by ASD can be calculated after collecting measurement data from at least two different phase angles.

[0018] In a preferred embodiment of the invention, the DC current is injected intermittently in the form of a finite injection period followed by a waiting period until the next DC current injection.

[0019] In a preferred embodiment of the invention, the durations of both the injection period and the waiting period can be variable and synchronized with the rotational speed of the motor. This embodiment is explicitly applied only when the motor is running.

[0020] In a preferred embodiment of the invention, if the ASD is not in a safe operating state, the injection of DC current is stopped. An unsafe operating state can be defined as including faults, tripping, reaching limits, and / or various derating conditions of the motor and / or ASD.

[0021] In a preferred embodiment of the invention, if the ASD operates in an over-dynamic state that affects the extraction of the DC component present in the determined output current and voltage, the injection of DC current is stopped.

[0022] In a preferred embodiment of the invention, the resistance Rs calculated on each phase is fed back into the ASD and used to update the ASD reference, control parameters, and / or control settings.

[0023] In a preferred embodiment of the invention, feedback is used to improve the control performance and / or stability of the ASD during operation, and / or feedback is used for predictive maintenance to detect faults in cables and / or motors, and / or incorrect installation.

[0024] Typically, new functionalities related to this invention can be implemented. These new functionalities may include predictive maintenance, wherein weak or loose phase connections and / or damaged or weak cables in one phase, as well as incorrect motor connections or wiring, can be detected prior to serious failures of the ASD and / or the motor.

[0025] Additional new features can be implemented in ASD to support debugging. This facilitates the detection of incorrect motor connections or wiring. This prevents future problems and potential cable or motor damage during motor operation.

[0026] During commissioning, ASD can calculate the resistance Rs on each phase of the motor and assess whether the difference between the resistances Rs of each phase is too high. Based on the difference between the resistances Rs, ASD can then send signals suggesting checks on the motor and / or cables. All of this can be done before the motor is run, thus avoiding application problems when the motor is running with and / or driving other equipment.

[0027] Another novel feature offered by this invention is support for troubleshooting motors driven by ASD. ASD can monitor and record the resistance Rs on each phase during operation. The recorded resistance Rs may be associated with conditions such as excessive torque, speed fluctuations, and / or other motor defects, all of which may be affected by unbalanced resistance.

[0028] The present invention also relates to an ASD for performing the methods described above. The ASD may include any hardware components required to perform the methods described above. Attached Figure Description

[0029] Further details and advantages of the invention will be described with reference to the following figures:

[0030] Figure 1 : Single-phase electrical diagram of an induction motor;

[0031] Figure 2 : Single-phase electrical diagram of an induction motor under DC power;

[0032] Figure 3 A simplified electrical diagram of an induction motor with all three-phase resistors;

[0033] Figure 4 : The electrical diagram of the ASD that injects DC current into the motor, and the space vector representation of the current;

[0034] Figure 5 Space vector representation of DC current injected in different directions: a) Direction 1, b) Direction 2;

[0035] Figure 6 A diagram illustrating the method of injecting DC current in two different directions and then solving for the unknowns Rs1, 2, and 3.

[0036] Figure 7 : The main components used to calculate the asymmetrical DC resistances Rs1, 2, 3; and

[0037] Figure 8 A brief overview of motors and ASD. Detailed Implementation

[0038] Before going into more details of the invention, some background information will be provided regarding the motor 20 used in the context of the invention. Figure 1 An electrical model of an electric motor 20 (e.g., an induction motor) controlled by an adjustable speed drive (ASD) 1 is shown, which is further described below. Figure 1 The single-phase diagram of the electric motor 20 is shown. It is assumed that the components on all three phases of the motor 20 are symmetrical, where Rs and Rr are the stator resistance and rotor resistance, respectively, Lls and Llr are the stator leakage inductance and rotor leakage inductance, respectively, Lm is the magnetizing inductance and Rfe is the equivalent iron loss resistance.

[0039] The stator voltage equation for the induction motor (electric motor 20) is:

[0040]

[0041] in

[0042] R s =Stator resistance

[0043] u s = Stator voltage applied by ASD 1

[0044] i s =Stator current source generated by ASD 1

[0045] ψ s =Stator flux

[0046] When only a DC signal is injected into a machine or motor, the derivative of the flux becomes zero, such as Figure 2 The neutralization equation 2 is given.

[0047] u s (t)=R s ·i s (t) (Equation 2)

[0048] As can be seen from ASD 1, the impedance of the induction motor to the DC input in steady state is R given in Equation 3. sDC .

[0049]

[0050] Therefore, if a small DC voltage bias can be superimposed on the motor supply voltage to inject a DC current component, the determined DC components of the voltage and current can be used to estimate the resistance Rs online. The estimation based on the DC model is independent of all motor parameters and is unaffected by inherent motor asymmetry.

[0051] The following paragraphs will provide further details regarding the identification of asymmetries in the given motor 20. Equation 2, given above, describes the motor equations for the assumed equilibrium model.

[0052] In the case of parameter imbalance, the equation is described in this form:

[0053]

[0054] The subscripts indicate the motor phase, such as 1 for phase U, 2 for phase V, and 3 for phase W. And it is assumed that... Figure 3 The DC signal injection method shown, Rs 1，2，3 Rk represents the internal ASD contact resistance. 1，2，3 Cable resistance Rc 1，2，3 and motor resistance Rm 1，2，3 The cumulative series resistance. Figure 3 This is a simplified electrical diagram of an electric motor 20 (particularly an induction motor) showing all three-phase resistances and their components.

[0055] ASD1 includes a power card 2 and a control card 3. Power card 2 can be connected to the AC grip power supply and provide power to motor 20. Control card 3 can be used to determine the voltage (us) mentioned above. 123 Three voltage estimates. Control card 3 may also include or be connected to determine the current is. 123 Three current sensors. Based on current is 123 and voltage us123 Given the determined value, control card 3 can calculate the corresponding three-phase cumulative resistance Rs. 123 .

[0056] Figure 4 An electrical diagram of ASD1, which injects DC current into the previously shown motor 20, and a space vector representation of the current are shown.

[0057] Some challenges have arisen in practice and Figure 4 Chinese instructions:

[0058] • ASD 1 cannot access the neutral point N of motor 20, but has its own internal reference point M, and therefore the common voltage U NM It exists between M and N.

[0059] • There is background DC offset in both voltage and current caused by physical devices, analog-to-digital converters, operational amplifiers, etc.

[0060] The output voltage system is three-phase and three-wire, which means there are only two independent equations.

[0061]

[0062] The following steps will be taken to compensate for the above problems:

[0063] a. Eliminating the offset: This is done by injecting currents in the same direction but with different signs and differentiating the equation.

[0064]

[0065] The result is simplified to this form:

[0066]

[0067] b. Eliminate common-mode voltage U MN This is accomplished by differentiating between phases (e.g., 1-2, 2-3, 3-1).

[0068]

[0069] By R s1 R s2 R s3 Let x1, x2, and x3 be the terms to be solved. The equation is simplified to this form:

[0070]

[0071] This equation cannot be solved because the known terms (current and voltage) are not independent:

[0072]

[0073] c. Solve the equations by adding more data sets. This is done by injecting current in different directions, thus collecting more data to form a dataset capable of solving for the unknown R. s1 R s2 R s3 It was accomplished by a system of independent equations. Figure 5 and Figure 6 The diagram is shown below.

[0074] Injection in direction 1:

[0075]

[0076] Injection in direction 2:

[0077]

[0078] The equations can be solved from different directions using either of these two datasets. An example of solving x1 and x2 is shown below. Similarities can be found in other different equations.

[0079]

[0080] Given two datasets from different directions, there are several possibilities for solving the same unknowns x1, x2, and x3. Therefore, to improve robustness relative to numerical errors, all possible equations can be solved for the same solution, and the results can be averaged.

[0081] Alternatively, different combinations of directions can be used (e.g., alternating directions d1 and d2) and Rs1, 2, 3 can be solved, then Rs1, 2, 3 can be injected along directions 2 and 3 and Rs1, 2, 3 can be solved again.

[0082] Figure 6 The diagram illustrates a method for injecting DC current in two different directions and then solving for the unknowns Rs1, 2, and 3.

[0083] Figure 7 The main components of ASD 1, which are shown, are capable of calculating the asymmetrical DC resistances Rs1, 2, 3 of motor 20 and their corresponding cable resistances Rc1, 2, 3, and the connections or wiring 19 thereto.

[0084] ASD 1 includes a power card 2 containing all the hardware needed to power motor 20 from the AC mains. Power card 2 may include analog circuitry, digital circuitry, and a power switch.

[0085] ASD 1 also includes a control card 3, which may include all the software, controllers and protection components of ASD 1. Figure 7 The ASD control unit 4, a sub-component of control card 3, is shown. ASD control unit 4 performs the main function of ASD 1, namely, controlling the movement of motor 20. ASD control unit 4 provides the hardware and control of all necessary features for motor control.

[0086] The second sub-component of control card 3 is Rs estimation block 5. Rs estimation block 5 may include an algorithm implemented in the control card software, which receives internal and external signals and calculates the motor connection resistance or motor wiring resistance for each phase Rs1, 2, 3. This information is fed back to the ASD control unit 4 to improve stability and control performance. In this invention, the term "block" may refer to a physical component and / or some software application or calculation process.

[0087] The subcomponent of Rs estimation block 5 includes Rs control unit 51, which provides the function of being responsible for the entire process of synchronizing (via the signal "synch") the injection of DC current and measuring the effects in the output current and voltage.

[0088] The injection is intermittent and can occur for only a short period of time. The injection can then be stopped and interrupted for a period of time until the next DC injection. This method minimizes fluctuations in the output motor torque and speed.

[0089] This function also estimates the correct timing of the injected DC current to avoid interfering with the system and causing faults and trips. This function also checks whether ASD 1 is in a steady-state and stable operating condition to perform DC measurements and avoid erroneous results.

[0090] Rs estimation block 5 also includes means for triggering or injecting DC current 52, including the reference I required for calculation. DCRef This is then sent to the ASD control unit 4 to generate a DC output current. This function injects the correct phase synchronization with the output current to avoid transients and erroneous results.

[0091] Rs estimation block 5 also includes methods for estimating voltage U. s123 The device 53 includes receiving the output voltage U from the ASD control unit 4. s1，2，3 And after filtering noise and compensating for inverter nonlinearity, from U DC1，2，3 Function to extract DC components.

[0092] Rs estimation block 5 also includes current sensor I s123 The device 54 includes receiving an output current I from an ASD current sensor. s1，2，3 And after filtering noise from IDC1，2，3 Function to extract DC components.

[0093] The asymmetric calculation of Rs is performed at computation block 55, which includes calculating R by solving equations 1 to 5 given above. s1，2，3 The algorithm.

[0094] Figure 8 A simplified overview of motor 20 and ASD 1 is shown.

[0095] Figure Labels

[0096] 1. Adjustable Speed ​​Drive (ASD)

[0097] 2. Electricity Card

[0098] 3. Control Card

[0099] 4ASD control unit

[0100] 5Rs estimation block

[0101] 19. Connection or wiring

[0102] 20 motors

[0103] 51 Rs control unit

[0104] 52 Devices for triggering or injecting DC current

[0105] 53. Device for estimating voltage Us123

[0106] 54 Current sensor Is123

[0107] 55 Calculation Blocks

Claims

1. A method for estimating the single-phase resistance of a motor controlled by a speed-adjustable drive while the motor is running and / or stopped, wherein the motor is an asynchronous motor or a synchronous motor, the method comprising the steps of: • Inject at least two DC currents into the motor as the output of the adjustable speed driver. • Determine the output voltage and current generated by the injected DC current. • Extract the DC component present in the determined output voltage and current, and • Calculate the cumulative output resistance Rs seen by the adjustable speed driver on each phase of the motor. The injected DC current is synchronized with the different phase angles of the basic output current of the adjustable speed driver.

2. The method according to claim 1, characterized in that, The determined output voltage and / or current are measured or estimated.

3. The method according to claim 1, characterized in that, The DC current is injected intermittently in a finite injection period followed by a waiting period until the next DC current injection.

4. The method according to claim 3, characterized in that, The duration of both the injection period and the waiting period can be varied and synchronized with the rotational speed of the motor.

5. The method according to claim 1, characterized in that, If the adjustable speed driver is not in a safe operating state, the injection of DC current shall be stopped.

6. The method according to claim 1, characterized in that, When the adjustable speed driver operates in an over-dynamic state that affects the extraction of the DC component present in the determined output current and voltage, the injection of the DC current is stopped.

7. The method according to claim 1, characterized in that, The calculated resistance Rs at each phase is fed back to the adjustable speed driver and used to update the adjustable speed driver reference, control parameters, and / or control settings.

8. The method according to claim 7, characterized in that, The feedback is used to improve the control performance and / or stability of the adjustable speed drive during operation, and / or the feedback is used for predictive maintenance to detect faults in cables and / or motors, and / or incorrect installation.

9. An adjustable speed drive for performing the method according to any one of the preceding claims.

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