A method for weakening magnetic field control of direct-drive permanent magnet generator

Abstract

The present invention relates to the field of control technology of three-phase converters of power systems, and in particular to a method for weak magnetic field control of a direct-drive permanent magnet generator, including a machine-side rotor flux orientation step and reactive current given value calculation; the reactive current given value calculation specifically includes the following steps: orienting the d-axis and q-axis rotor fluxes in a two-phase rotating coordinate system obtained by the machine-side rotor flux orientation step, and phase-locking to obtain the frequency; calculating impedance and related intermediate values; calculating the upper and lower limits of the torque converted by reactive power according to the steady-state weak magnetic field control equation of the permanent magnet synchronous motor in the rotating coordinate system, and obtaining the reactive current given value. Through this method, the problem that the existing weak magnetic field control method of synchronous motors is relatively complex can be effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of control of a three-phase converter of an electric power system, and in particular to a magnetic field weakening control method for a direct-drive permanent magnet generator. Background Art

[0002] Permanent magnet synchronous generators / motors have been widely used in wind power generation, electric vehicles and other high-demand occasions due to their high power density, high reliability and high efficiency. When the permanent magnet synchronous motor is running at high speed, the stator voltage will increase with the speed. It is necessary to use weak magnetic control technology to reduce the stator voltage to protect power electronic devices. It is very important to use weak magnetic control on permanent magnet synchronous motors to widen the speed range. The idea of ​​weak magnetic control of permanent magnet synchronous motors comes from the magnetic control of separately excited DC motors. The research on weak magnetic control of permanent magnet synchronous motors began in the mid-1980s. And a complete weak magnetic theory was formed in the early 1990s.

[0003] There are two main methods of synchronous motor weakening control currently used: one is based on field-oriented control (FOC), and the other is maximum torque per ampere (MTPA) control. MTPA control is mainly used to improve motor efficiency when running at low speed, while FOC control is mainly to design d-axis and q-axis current regulators. Common weakening control strategies include formula calculation method, table lookup method, gradient descent method, negative id compensation method, single current regulation method, current angle method, etc. The accuracy of the formula calculation method depends on the accuracy of the motor mathematical model. It is difficult to establish an accurate model in practice, so it is rarely used in actual engineering. The table lookup method uses a large amount of experimental data and makes a table, which reduces the real-time calculation amount of the motor control chip and is more complicated to implement. The gradient descent method has a large amount of calculation and is more complicated to implement. The negative id compensation method is simple to implement, but it cannot achieve weakening in the weakening area III. The current angle method cannot achieve weakening in the weakening area III. The single current regulation method uses voltage as the regulation object to achieve deep weakening, which has certain development prospects, but also has certain shortcomings and needs to be improved. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a direct-drive permanent magnet generator weak magnetic control method, which can effectively solve the problem that the existing synchronous motor weak magnetic control method is relatively complicated.

[0005] The present invention is achieved by adopting the following technical solutions:

[0006] A direct-drive permanent magnet generator weak magnetic field control method, characterized in that: it includes a machine-side rotor flux orientation step and reactive current set value calculation; the reactive current set value calculation specifically includes the following steps:

[0007] S 21 . Orient the d-axis and q-axis rotor fluxes in the two-phase rotating coordinate system obtained by the machine-side rotor flux orientation step, and phase-lock to obtain the frequency;

[0008] S 22 .Calculate impedance and related intermediate values;

[0009] S 23 .According to the steady-state weak magnetic control equation of the permanent magnet synchronous motor in the rotating coordinate system, the upper and lower limits of the torque converted by reactive power are calculated, and the reactive current given value is obtained.

[0010] The step of orienting the rotor flux on the machine side specifically includes the following steps:

[0011] S 11 .Convert the three-phase line voltage and current of the stator into the instantaneous voltage and current values ​​in the two-phase stationary coordinate system respectively;

[0012] S 12 . The rotor flux of the α and β axes in the two-phase stationary coordinate system is estimated by the mathematical model of the permanent magnet synchronous generator in the two-phase stationary coordinate system based on the instantaneous voltage and current in the two-phase stationary coordinate system;

[0013] S 13 .Perform coordinate rotation transformation on the rotor flux in the two-phase stationary coordinate system to transform the α-axis and β-axis rotor flux into the d-axis and q-axis rotor flux in the two-phase rotating coordinate system.

[0014] The step S 11 Specifically refers to: the three-phase line voltage v of the stator ab (t), v bc (t), v ca (t) is converted into the instantaneous voltage value u in the two-phase stationary coordinate system α 、u β , the three-phase current i of the stator a (t), i b (t), i c (t) is converted into the instantaneous current value i in the two-phase stationary coordinate system α 、i β ;in,

[0015]

[0016]

[0017] The step S 12 The rotor flux of the α and β axes in the two-phase stationary coordinate system is:

[0018]

[0019] Among them, ψ α , β is the rotor flux of the α and β axes in the two-phase stationary coordinate system, R s is the stator resistance, L d , L q is the stator inductance, u α 、u β are the instantaneous voltage values ​​of the two-phase stationary coordinate system, i α 、i β They are the instantaneous current values ​​in the two-phase stationary coordinate system.

[0020] The step S 13 In the two-phase rotating coordinate system, the d-axis and q-axis rotor fluxes are:

[0021]

[0022] Among them, ψ d , q is the d-axis and q-axis rotor flux in the two-phase rotating coordinate system, θ is the rotor electrical angle; ψ α , β is the rotor flux of α and β axes in the two-phase stationary coordinate system.

[0023] The relevant intermediate values ​​include the rotor electrical angular velocity ω and the back electromotive force U f ;in,

[0024] ω=2*π*f

[0025] U f =ωψ f

[0026] Where f is the frequency, ψ f is the permanent magnet flux.

[0027] The step S 23 The upper and lower limits of the torque converted by reactive power are:

[0028]

[0029]

[0030] in, The torque converted from reactive power; is the maximum allowable AC output voltage effective value of the inverter, U d , U q are the d-axis and q-axis components of the stator voltage in the two-phase rotating coordinate system; P = ωψ f I d is the active power, ψ f is the permanent magnet flux, Id is the d-axis component of the stator current in the two-phase rotating coordinate system; ωL d is the impedance; ω is the rotor electrical angular velocity; ψ d , q is the d-axis and q-axis rotor flux in the two-phase rotating coordinate system; R s is the stator resistance.

[0031] The step S 23 In the above, the reactive current given value is:

[0032]

[0033] Among them, I_ref is the reactive current given value, T q is the active torque given, is the torque converted from reactive power; ψ d , q is the d-axis and q-axis rotor flux in the two-phase rotating coordinate system.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] 1. The direct-drive permanent magnet generator weak magnetic control method described in the present invention has a simple calculation process, a small amount of calculation, is easy to implement in a program, requires few motor parameters, can achieve precise weak magnetic field, makes up for the shortcomings of traditional formula calculation method and table lookup method, and finds a good balance between the amount of calculation and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, wherein:

[0037] Figure 1 It is the coordinate transformation vector diagram of the three-phase stationary coordinate system, the two-phase stationary coordinate system and the two-phase rotating coordinate system. DETAILED DESCRIPTION

[0038] Example 1

[0039] As a basic implementation mode of the present invention, the present invention includes a direct-drive permanent magnet generator weak magnetic control method, including a machine-side rotor flux orientation step and a reactive current set value calculation. The reactive current set value calculation specifically includes the following steps:

[0040] S 21 .Orient the d-axis and q-axis rotor fluxes in the two-phase rotating coordinate system obtained through the machine-side rotor flux orientation step, and phase-lock to obtain the frequency.

[0041] S 22 .Calculate impedance and related intermediate values;

[0042] S23 .According to the steady-state weak magnetic control equation of the permanent magnet synchronous motor in the rotating coordinate system, the upper and lower limits of the torque converted by reactive power are calculated, and the reactive current given value is obtained.

[0043] Example 2

[0044] As a preferred embodiment of the present invention, the present invention includes a direct-drive permanent magnet generator weak magnetic control method, including a machine-side rotor flux orientation step and reactive current set value calculation.

[0045] The step of orienting the rotor flux on the machine side specifically includes the following steps:

[0046] S 11 .Convert the three-phase line voltage and current of the stator into the instantaneous voltage and current values ​​in the two-phase stationary coordinate system respectively;

[0047] S 12 . The rotor flux of the α and β axes in the two-phase stationary coordinate system is estimated by the mathematical model of the permanent magnet synchronous generator in the two-phase stationary coordinate system based on the instantaneous voltage and current in the two-phase stationary coordinate system;

[0048] S 13 .Perform coordinate rotation transformation on the rotor flux in the two-phase stationary coordinate system to transform the α-axis and β-axis rotor flux into the d-axis and q-axis rotor flux in the two-phase rotating coordinate system.

[0049] The reactive current given value calculation specifically includes the following steps:

[0050] S 21 . Orient the d-axis and q-axis rotor fluxes in the two-phase rotating coordinate system obtained by the machine-side rotor flux orientation step, and phase-lock to obtain the frequency;

[0051] S 22 .Calculate impedance and related intermediate values;

[0052] S 23 .According to the steady-state weak magnetic control equation of the permanent magnet synchronous motor in the rotating coordinate system, the upper and lower limits of the torque converted by reactive power are calculated, and the reactive current given value is obtained.

[0053] Example 3

[0054] As the best embodiment of the present invention, refer to the attached specification. Figure 1 The present invention includes a direct-drive permanent magnet generator weak magnetic control method, including a machine-side rotor flux orientation step and reactive current given limit value calculation.

[0055] The step of orienting the rotor flux on the machine side specifically includes the following steps:

[0056] S 11.The three-phase line voltage v of the stator ab (t), v bc (t), v ca (t) is converted into the instantaneous voltage value u in the two-phase stationary coordinate system α 、u β , the three-phase current i of the stator a (t), i b (t), i c (t) is converted into the instantaneous current value i in the two-phase stationary coordinate system α 、i β .in,

[0057]

[0058]

[0059] S 12 .Based on the instantaneous values ​​of voltage and current in the two-phase stationary coordinate system, the α and β axis rotor flux in the two-phase stationary coordinate system is estimated through the mathematical model of the permanent magnet synchronous generator in the two-phase stationary coordinate system.

[0060] Among them, the mathematical model of the permanent magnet synchronous generator in the two-phase stationary coordinate system is:

[0061]

[0062] Among them, R s is the stator resistance, ψ α , β is the rotor flux in the two-phase stationary coordinate system, L d , L q is the stator inductance, ψ f is the permanent magnet flux, θ is the rotor electrical angle, u α 、u β are the instantaneous values ​​of the stator voltage in the two-phase stationary coordinate system, i α 、i β They are the instantaneous current values ​​in the two-phase stationary coordinate system.

[0063] After mathematical transformation, we can get:

[0064]

[0065] Integrating both sides of the above equation, we can get the rotor flux of the α and β axes in the two-phase stationary coordinate system:

[0066]

[0067] Among them, ψ α , β is the rotor flux of α and β axes in the two-phase stationary coordinate system.

[0068] S 13 . Perform coordinate rotation transformation on the rotor flux in the two-phase stationary coordinate system to transform the α-axis and β-axis rotor flux into the d-axis and q-axis rotor flux in the two-phase rotating coordinate system:

[0069]

[0070] Where θ is the rotor electrical angle; ψ α , β is the rotor flux of α and β axes in the two-phase stationary coordinate system.

[0071] The reactive current given limit value calculation specifically includes the following steps:

[0072] S 21 . Orient the d and q axis rotor flux in the two-phase rotating coordinate system obtained by the machine-side rotor flux orientation step, and phase-lock to obtain the frequency. This technology is a conventional technology in the field, and those skilled in the art can easily achieve orientation and phase-lock to obtain the frequency, so it will not be described in detail.

[0073] S 22 . Calculate impedance and related intermediate values, including rotor electrical angular velocity ω and back electromotive force U f ,in,

[0074] ω=2*π*f

[0075] U f =ωψ f

[0076] Where f is the frequency, ψ f is the permanent magnet flux.

[0077] S 23 .According to the steady-state weak magnetic control equation of the permanent magnet synchronous motor in the rotating coordinate system, the upper and lower limits of the torque converted by reactive power are calculated, and the reactive current given value is obtained.

[0078] Among them, the mathematical model of permanent magnet synchronous motor is:

[0079] ωψ f (U d +jU q )=R s ωψ f I d +jωL q ωψ f I d +(jR s -ωL d )ωψ f I q +ωψ f ωψf

[0080] Where ω is the rotor electrical angular velocity, ψ f is the permanent magnet flux, R s is the stator resistance, U d , U q is the dq axis component of the stator voltage in the two-phase rotating coordinate system, I d ,I q is the dq-axis component of the stator current in the two-phase rotating coordinate system.

[0081] After mathematical transformation, we can get:

[0082]

[0083] Where P = ωψ f I d , is the active power, Q=-ωψ f I q , is the reactive power, ω is the rotor electrical angular velocity, ψ f is the permanent magnet flux, R s is the stator resistance, U d , U q is the dq axis component of the stator voltage in the two-phase rotating coordinate system, I d ,I q is the dq axis component of the stator current in the two-phase rotating coordinate system, L d , L q is the stator inductance.

[0084] Multiply both sides of the equation We can get:

[0085]

[0086] Shift the items to get:

[0087]

[0088] Modulo we get:

[0089]

[0090] in, It is the maximum allowable AC output voltage effective value of the inverter.

[0091] Transpose and divide After that, you can get

[0092]

[0093]

[0094] Permanent magnet synchronous motor Ld With L q Close, L d -L q ≈0, combined The upper and lower limits of reactive torque can be derived:

[0095]

[0096]

[0097] The reactive current is given by:

[0098]

[0099] Among them, T q is the active torque given, is the torque given by reactive power conversion, ψ d , q is the d-axis and q-axis rotor flux in the two-phase rotating coordinate system.

[0100] This embodiment has been successfully applied to a 3.2MW direct-drive permanent magnet synchronous generator set, and the magnetic weakening effect is very good.

[0101] In summary, after reading the present invention document, ordinary technicians in this field can make various other corresponding transformation schemes based on the technical scheme and technical concept of the present invention without creative mental labor, which all fall within the scope of protection of the present invention.

Claims

1. A method for weakening magnetic field of a direct-drive permanent magnet generator, characterized in that: The method includes the steps of machine-side rotor flux orientation and reactive current given value calculation; the reactive current given value calculation specifically includes the following steps: S 21 . Orient the d-axis and q-axis rotor fluxes in the two-phase rotating coordinate system obtained by the machine-side rotor flux orientation step, and phase-lock to obtain the frequency; S 22 . Calculate impedance and related intermediate values; the related intermediate values ​​include rotor electrical angular velocity ω and back electromotive force U f ; S 23 . According to the steady-state weak magnetic control equation of the permanent magnet synchronous motor in the rotating coordinate system, the upper and lower limits of the torque converted by reactive power are calculated, and the reactive current given value is obtained; Among them, the calculation method of the upper and lower limits of the torque converted by reactive power is: in, The torque converted from reactive power; is the maximum allowable AC output voltage effective value of the inverter, U d , U q are the d-axis and q-axis components of the stator voltage in the two-phase rotating coordinate system; P = ωψ f I d is the active power, ψ f is the permanent magnet flux, I d is the d-axis component of the stator current in the two-phase rotating coordinate system; ωL d is the impedance; d , q is the d-axis and q-axis rotor flux in the two-phase rotating coordinate system; R s is the stator resistance; The calculation method of reactive current given value is: Among them, I_ref is the reactive current given value, T q is the active torque given.

2. A direct-drive permanent magnet generator weak magnetic field control method according to claim 1, characterized in that: The step of orienting the rotor flux on the machine side specifically includes the following steps: S 11 .Convert the three-phase line voltage and current of the stator into the instantaneous voltage and current values ​​in the two-phase stationary coordinate system respectively; S 12 . The rotor flux of the α and β axes in the two-phase stationary coordinate system is estimated by the mathematical model of the permanent magnet synchronous generator in the two-phase stationary coordinate system based on the instantaneous voltage and current in the two-phase stationary coordinate system; S 13 .Perform coordinate rotation transformation on the rotor flux in the two-phase stationary coordinate system to transform the α-axis and β-axis rotor flux into the d-axis and q-axis rotor flux in the two-phase rotating coordinate system.

3. A direct-drive permanent magnet generator weak magnetic field control method according to claim 2, characterized in that: The step S 11 Specifically refers to: the three-phase line voltage v of the stator ab (t), v bc (t), v ca (t) is converted into the instantaneous voltage value u in the two-phase stationary coordinate system α 、u β , the three-phase current i of the stator a (t), i b (t), i c (t) is converted into the instantaneous current value i in the two-phase stationary coordinate system α 、i β ; in, 4. A direct-drive permanent magnet generator weak magnetic field control method according to claim 3, characterized in that: The step S 12 The rotor flux of the α and β axes in the two-phase stationary coordinate system is: Among them, ψ α , β is the rotor flux of the α and β axes in the two-phase stationary coordinate system, R s is the stator resistance, L d , L q is the stator inductance, u α 、u β are the instantaneous voltage values ​​of the two-phase stationary coordinate system, i α 、i β They are the instantaneous current values ​​in the two-phase stationary coordinate system.

5. A direct-drive permanent magnet generator weak magnetic field control method according to claim 4, characterized in that: The step S 13 In the two-phase rotating coordinate system, the d-axis and q-axis rotor fluxes are: Among them, ψ d , q is the d-axis and q-axis rotor flux in the two-phase rotating coordinate system, θ is the rotor electrical angle; ψ α , β is the rotor flux of α and β axes in the two-phase stationary coordinate system.

6. A direct-drive permanent magnet generator weak magnetic field control method according to claim 1 or 5, characterized in that: ω=2*π*f U f =oops f Where f is the frequency, ψ f is the permanent magnet flux.

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