专利汇可以提供Method and system for estimating rotor angular position and rotor angular velocity at low speeds or standstill专利检索,专利查询,专利分析的服务。并且A method and system for estimating an angular position and an angular velocity of a rotor in a dynamoelectric machine measures an AC current and a potential for each of a plurality of windings coupled to a stator of the dynamoelectric machine, transforms the measured currents and potentials to a stationary frame to produce transformed currents and transformed potentials, and processes the transformed currents and transformed potentials to produce a first intermediate signal and a second intermediate signal. The first intermediate signal and the second intermediate signal are cross-coupled by being processed to obtain a first extended rotor flux value and a second extended rotor flux value that are each functions of the first intermediate signal and the second intermediate signal. The first extended rotor flux value and the second extended rotor flux value are applied to a phase lock loop to derive an estimated rotor angular position and an estimated rotor angular velocity for the dynamoelectric machine.,下面是Method and system for estimating rotor angular position and rotor angular velocity at low speeds or standstill专利的具体信息内容。
What is claimed is:
This invention relates to rotor angular position and velocity sensing systems for mechanical shaft sensorless control of dynamoelectric machines, and more particularly to an improved system for resolving the position and velocity of a rotor for a dynamoelectric machine using an estimate of extended rotor flux.
In some vehicles, including some aircraft, a motor may be utilized both as a motor and as a generator. Because of this dual function, the motor may be called a dynamoelectric machine. A typical motor comprises a stationary stator, and a rotating rotor. In some motors, it is necessary to detect a position of a rotor in order to sustain operation of the motor. Determining a rotor position typically requires a shaft position sensor. It is desirable to eliminate a mechanical shaft sensor to reduce cost and improve reliability.
Some methods of sensorless rotor position detection include the back EMF method, which determines rotor position based on voltage, the signal injection method, which injects high frequencies into a system, and the method discussed in U.S. Pat. No. 7,072,790 which uses flux to determine rotor position. It is desirable to improve the method U.S. Pat. No. 7,072,790 for applications operating at low speeds or at a standstill.
A method and system for estimating an angular position and an angular velocity of a rotor in a dynamoelectric machine measures an AC current and a potential for each of a plurality of windings coupled to a stator of the dynamoelectric machine, transforms the measured currents and potentials to a stationary frame to produce transformed currents and transformed potentials, and processes the transformed currents and transformed potentials to produce a first intermediate signal and a second intermediate signal. The first intermediate signal and the second intermediate signal are cross-coupled by being processed to obtain a first extended rotor flux value and a second extended rotor flux value that are each functions of the first intermediate signal and the second intermediate signal. The first extended rotor flux value and the second extended rotor flux value are applied to a phase lock loop to derive an estimated rotor angular position and an estimated rotor angular velocity for the dynamoelectric machine.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.
As shown in
To start the motor 12, an AC power supply 16 provides an AC voltage along supply lines 18 to a rotating exciter 19. In the example of
The AC voltage from the supply lines 18 induces an AC voltage along motor terminals 20a, 20b, and 20c. The induced voltage causes a current to flow through an output filter 22. A microprocessor 24 measures a voltage 26 and a current 28 from each of the terminals 20a, 20b, and 20c. A position and speed estimator 30 uses the voltage and current measurements to estimate a flux of the motor 12 and to estimate a rotor position 32 and a rotor angular velocity 34.
Once the estimated rotor position 32 and estimated rotor angular velocity 34 have been calculated, an inverter 38 is turned ON. The microprocessor 24 processes the estimated rotor position 32 and estimated rotor angular velocity 34 to control a pulse width modulated (PWM) generator 36. An inverter 38 is coupled to the PWM generator 36 and converts a DC voltage from DC voltage supply lines 40 to AC. This voltage enables AC to flow through the output filter 22, which improves power quality by filtering out harmonics and reducing electromagnetic interference (EMI). The AC from the terminals 20a, 20b, and 20c then flows to a stator of the motor 12 to sustain operation of the motor 12.
Proportional and integral (PI) regulators 47 and 48 process the differences ΔId and ΔIq using proportional and integral gains, and transmit an output signal to d-q to alpha-beta frame transformer 50, which converts the output into a stationary α-β frame to produce Valpha* and Vbeta* signals which are transmitted to the PWM generator 36. The PWM generator then controls the inverter 38 accordingly to produce a desired AC voltage.
The output filter 22 comprises an inductor and a capacitor (not shown) in each phase. An input current Iinvt flows from the inverter 38 along the windings 23a, 23b, and 23c to the output filter 22, and an output current Is flows from the output filter 22 along the terminals 20a, 20b, and 20c to the motor 12. The current flowing through the capacitor can be calculated by the following equation:
where Îc is an estimated capacitor current; and
A motor current can then be calculated using the following equation:
Is=Iinvt−Îc equation #2
where Is is the calculated motor current; and
Equations 1 and 2 apply to all three phases A, B, and C corresponding to the three windings 20a, 20b, and 20c.
The voltage measurements 26 and current measurements 28 are measured from each of the three terminals (20a, 20b, 20c) and each of the three windings (23a, 23b, 23c) in an a-b-c frame. The current measurement 28 is a measurement of the inverter output current Iinvt. A flux estimation is implemented in an alpha-beta (α-β) stationary frame. The relationship between the α-β frame and the a-b-c frame is described in the following equation:
where f can be replaced with voltage, current, or flux;
The stationary α-β frame is a two phase frame and is a necessary step in calculating flux. Equation #3 is used to determine an α-axis voltage Vα, a β-axis voltage Vβ, an α-axis current Iα, and a β-axis current Iβ.
The following equation can then be used to determine an extended rotor flux in the α-β stationary frame:
where λext
Equation #4 can be used to determine flux in both salience and non-salience motors. As shown in equation #4, an integrator 1/s is required to calculate extended rotor flux. The integrator 1/s is an operator, not a variable.
One problem that may arise when using a pure integrator, such as “1/s”, is a DC drift problem, in which a small DC component in an AC signal can cause a substantial error in a flux determination. To avoid the DC drift problem associated with a pure integrator, lag functions, such as
may be used, as shown in the following equation:
where ωi is a selected corner frequency.
A flux λs in the stator of the motor 12 is represented by a phasor 60. A stator current Is is represented by a phasor 62. A stator potential Vs is represented by a phasor 64. A phasor 66 represents Is*Lq where Lq is a q-axis rotor inductance. A vector sum of the phasor 60, representing λs, and the phasor 66, representing Is*Lq, is an extended rotor flux λext, which aligns with the d-axis of the d-q frame, and is represented by a phasor 67.
A back electromotive force (EMF) Es is represented by a phasor 68. As shown in
An extended back electromotive force (EEMF), Eext, in the stator is represented by a phasor 72, and aligns with the q-axis of the d-q frame. Is*Xq, where Xq is a q-axis stator reactance, is represented by a phasor 74. The extended back EMF represented by phasor 72 is a vector sum of Es represented by phasor 68 and Is*Xq represented by a phasor 74.
first lag function 92 to produce
on a signal path 93.
on the signal path 93 is multiplied by a
second lag function 94 to produce
on a signal path 95.
Additionally, a transformed measured current Iβ for the β-axis on a signal path 96 is multiplied by the stator resistance Rs 98 to produce Iβ*Rs on a signal path 100. A summer 102 subtracts Iβ*Rs on the signal path 100 from the transformed potential Vβ on a signal path 104 to produce Vβ−(Iβ*Rs) on a signal path 106. Vβ−(Iβ*Rs) on the signal path 106 is multiplied by the
first lag function 108 to produce
on a signal path 110.
on the signal path 110 is multiplied by the
second lag function 112 to produce
on a signal path 114.
The transformed measured current Iα for the α-axis on the signal path 80 is also multiplied by a q-axis inductance Lq 116 to produce Iα*Lq on the signal path 118. A summer 120 subtracts Iα*Lq on the signal path 118 from
on the signal path 93 and adds
from the signal path 114 to produce
which corresponds to the extended rotor flux on the α-axis {circumflex over (λ)}ext
Additionally, the transformed measured current Iβ for the β-axis on the signal path 96 is also multiplied by a q-axis inductance Lq 124 to produce Iβ*Lq on the signal path 126. A summer 128 subtracts Iβ*Lq on the signal path 126 from
on the signal path 110 and subtracts
on the signal path 95 from
on the signal path 110 to produce
which corresponds to the extended rotor flux on the β-axis {circumflex over (λ)}ext
As shown in
The following equation can be used to describe the relationship between the extended rotor flux and the rotor position:
where θ is the rotor position; and
Using equation #6, it would be possible to use an arctangent function to calculate a rotor position. Another option is to used a phase-locked loop (PLL) to derive position and angular velocity information.
A summer 148 subtracts the α-axis multiplier output signal on the signal path 138 from the β-axis multiplier output signal on the signal path 146 to produce a difference signal on a signal path 150. A proportional and integral (PI) regulator function 152 multiplies the difference signal on the signal path 150 by the function
to produce a PI output signal on a signal path 154. Ki is an integral gain of the PI function 152, and Kp is a proportional gain of the PI function 152. Both Ki and Kp are constants based on a design of the system 10 as shown in
An integral function 156 multiplies the PI output signal on the signal path 154 by the function 1/s to produce an integration output signal on a signal path 158. The integration output signal on the signal path 158 is also fed into the inputs of the sine function 136 and the cosine function 144 to provide the PLL.
A low pass filter (LPF) function 160 multiplies the PI output signal on the signal path 154 by a third lag function
to produce an estimated rotor angular velocity {circumflex over (ω)} on a signal line 162, where ωc is a corner or cutoff frequency of the LPF function 160. A low pass filter associated with the LPF function 160 is used to smooth out the signal on the signal line 154.
The integration output signal on the signal path 158 is compensated by an offset Δθ to obtain a final estimated rotor angular position {circumflex over (θ)}. The offset Δθ can be a lump-sum error of miscellaneous delays, including delays introduced by the lag functions 92, 108 of the
When the motor 12 is at a standstill, as magnetic flux in the motor 12 changes in magnitude, a voltage is induced on the motor terminals 20a, 20b, and 20c, which can be sensed by the microprocessor 24. The induced stator voltages in the α-β frame can be described by the following equation:
where λs is a magnitude of stator flux; and
The measured voltage 26 can be transformed to an alpha-beta frame. The transformed measured voltages Vα and Vβ may be fed into the PLL as shown in
During an initial time period 196, the AC power supply 16 is OFF, and the three voltages 190, 192, and 194 voltage close to zero and the estimated rotor position θ0 200 cannot be used to determine actual rotor position. At time 198, the AC power supply 16 turns ON and current flows to the rotating exciter 19 through the supply line 18 in the system 10. During this period, an excitation magnetic field of the motor 12 is arising. The rising magnetic flux induces voltage at the terminals 20a, 20b, and 20c of the system 10. The magnitude of voltages 190, 192 and 194 is sufficient for the microprocessor 24 to be able to estimate rotor position θ0 200. In graph 188, from time 198 to approximately time 202 the value of θ0 remains stable, and after time 202 the value starts to fluctuate due to a decaying voltage signal as shown in graph 186. This stable period demonstrates that a rotor position can be estimated from the voltages 190, 192, and 194 during the stable time period.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
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