A coordinated control method for minimum copper loss in permanent magnet motor systems

Abstract

The present invention discloses a method for coordinated control of minimum copper loss in a permanent magnet motor system, comprising the following steps: S1, based on the topological structure of an AC excitation high-efficiency generator (HESG) and its magnetic modulation principle, obtaining a physical model of the motor in a d-q rotating coordinate system, and deriving the voltage equation, flux equation, and electromagnetic torque equation in the d-q coordinate system; S2, based on the magnetic modulation and speed expansion requirements in low-speed and high-speed operation stages, respectively deriving the Lagrange equations under different constraints; S3, with minimizing motor copper loss as the optimization goal, online allocating excitation current and armature current to achieve coordinated control of the excitation current and armature current. The present invention can achieve online allocation of excitation current and armature current, obtain minimum copper loss, and improve the efficiency of the power generation system.

Description

Technical Field

[0001] The present invention relates to the technical field of excitation motors, and in particular to a minimum copper loss coordinated control method for a permanent magnet motor system. Background Art

[0002] A hybrid-excitation synchronous generator (HESG) organically combines the magnetic potential of the electric excitation field and the magnetic potential of the permanent magnet. By controlling the excitation current, it can effectively regulate the air gap magnetic field. Traditional hybrid-excitation motors place the excitation winding on the rotor and require connection to a DC power supply via brushes and slip rings. This results in low reliability and is unsuitable for high-speed operation. Meanwhile, AC-excited HESGs place the excitation winding on the stator and, by using AC excitation, achieve simple brushless excitation, resulting in a simple and reliable structure.

[0003] Currently, traditional hybrid excitation DC power generation system control methods are mainly divided into two categories. The first type is to control the excitation current separately. The excitation converter generates a three-phase symmetrical excitation current, which regulates the motor air gap magnetic field to achieve DC regulated output voltage. The second type is to control the armature current separately. The excitation current remains unchanged, and the armature winding is connected to a PWM rectifier to maintain a stable output voltage. However, neither of these methods can fully utilize the power output capacity of the AC-excited HESG. Existing current coordinated control methods are mainly targeted at hybrid excitation motor drive systems, and there is little research on coordinated control strategies for hybrid excitation DC power generation systems. Summary of the Invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method for coordinated control of minimum copper loss in a permanent magnet motor system, to achieve online distribution of excitation and armature currents, to give full play to the power output capacity of the AC excitation HESG, and to achieve voltage-stabilized operation in a wide speed range.

[0005] Technical solution: The minimum copper loss coordinated control method of the permanent magnet motor system of the present invention comprises the following steps:

[0006] S1. Based on the topological structure of the AC-excited HESG and its magnetic regulation principle, the physical model of the motor in the dq rotating coordinate system is obtained, and the voltage equation, flux equation, and electromagnetic torque equation in the dq coordinate system are derived;

[0007] S2, based on the requirements of magnetic adjustment and speed expansion in low-speed and high-speed operation stages, the Lagrangian equations under different constraints are derived respectively;

[0008] S3, with the minimum copper loss of the motor as the optimization goal, distributes the excitation current and armature current online to achieve coordinated control of the excitation current and armature current.

[0009] Furthermore, step S1 specifically includes:

[0010] Assuming that the AC excitation HESG is an ideal motor, when a positive current flows through the three-phase armature winding, a positive flux is generated. When a positive current flows through the three-phase excitation winding, a positive flux is generated. From this, the voltage equation, flux equation, and electromagnetic torque equation in the dq coordinate system can be obtained as follows:

[0011] Voltage equation:

[0012]

[0013] Where, subscripts s and f represent the parameters of armature winding and excitation winding respectively; subscripts d and q represent the parameters of d-axis and q-axis respectively; ψ df , ψ qf Respectively represent the d-axis and q-axis magnetic flux of the excitation winding; ψ ds , ψ qs Represent the armature winding d-axis and q-axis magnetic flux respectively; i df 、i qf are the d-axis and q-axis components of the excitation current respectively; i ds 、i qs are the d-axis and q-axis components of the armature current respectively; u df 、u qf are the d-axis and q-axis components of the excitation voltage respectively; u ds 、u qs are the d-axis and q-axis components of the armature voltage respectively;

[0014] Magnetic flux equation:

[0015]

[0016] Electromagnetic torque equation:

[0017]

[0018] Where p is the differential operator; T em is the electromagnetic torque; ω is the synchronous angular frequency of the motor; R s , R f are the internal resistances of the armature winding and the field winding respectively; L ds , L qs They are the armature winding d-axis self-inductance and q-axis self-inductance, L df , L qf are the d-axis self-inductance and q-axis self-inductance of the excitation winding respectively; L dm is the mutual inductance between the field winding and the armature winding d-axis; L qm is the mutual inductance between the excitation winding and the armature winding q axis; ψ pms and ψ pm are the permanent magnet flux amplitudes on the armature winding and the excitation winding respectively; n ps , n pf are the number of pole pairs of the armature winding and the field winding respectively.

[0019] Furthermore, the step S2 specifically includes: when the AC excitation HESG runs at high speed, the armature winding dq axis voltage equation is:

[0020]

[0021] And should meet the following requirements:

[0022]

[0023] Where i fmax is the current limit value of the excitation winding;

[0024] The dq axis current constraints are obtained:

[0025]

[0026] Ignoring the switching loss of the PWM rectifier, the output electromagnetic power P of the AC excitation HESG is e and the total power consumed by the load P load It is expressed as follows:

[0027]

[0028] Furthermore, the DC bus voltage equation is:

[0029]

[0030] Among them, U dc is the output DC voltage reference value; R is the DC load;

[0031] The Lagrange equation during high-speed operation is:

[0032]

[0033] Where λ1 and λ2 are Lagrange multipliers;

[0034] In the low speed operation stage, the armature current magnetic component i ds Set to 0A, the Lagrange equation is expressed as follows:

[0035]

[0036] Where λ is the Lagrange multiplier.

[0037] Furthermore, the step S3 specifically includes: the objective function of the minimum copper loss control is:

[0038]

[0039] With the goal of minimizing copper loss, the optimal distribution of excitation current and armature current is obtained; the Lagrange multiplier method is used to solve the optimal solution of each reference current.

[0040] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0041] 1. Based on the magnetic adjustment and speed expansion requirements in high-speed and low-speed operation stages, the present invention derives the Lagrange equations under different constraints, giving full play to the power output capacity of the AC excitation HESG;

[0042] 2. Compared to hybrid excitation motor control methods that only control the excitation or armature current to regulate the air gap magnetic field, the present invention's coordinated control strategy for excitation and armature current, with the goal of minimizing copper loss, can fully utilize the hybrid excitation motor's two windings, improve the power density of the power generation system, and achieve wide-speed operation of the hybrid excitation motor.

[0043] 3. The coordinated control strategy of excitation and armature current proposed in the present invention with the minimum copper loss as the optimization goal can coordinate the allocation of excitation and armature current according to the real-time operating status of the system. Experimental results show that compared with the traditional current control strategy, its speed range can be increased by up to 3.9 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is the block diagram of the current coordinated control of the AC excitation HESG;

[0045] Figure 2 This is the electromagnetic constraint diagram of AC excitation HESG;

[0046] Figure 3 Schematic diagram of the AC excitation HESG physical model;

[0047] Figure 4 (a) is a comparison chart of the variable speed voltage stabilization test results of controlling the excitation current alone.

[0048] (b) is a comparison chart of the variable speed voltage stabilization experiment results of controlling the armature current alone.

[0049] (c) is a comparison chart of the low-speed operation experimental results of current coordinated control.

[0050] (d) is a comparison chart of the current coordinated control high-speed operation experimental results.

[0051] (e) is a comparison chart of copper consumption at different speeds. DETAILED DESCRIPTION

[0052] The present invention will be described in further detail below with reference to the accompanying drawings and specific implementations.

[0053] like Figure 1The figure shows a flow chart of the minimum copper loss coordinated control method for the permanent magnet motor system of this embodiment. The excitation winding and armature winding are each connected to a set of controllable power converters. The error between the given output DC voltage command value and the actual value measured by the voltage sensor is input into the voltage loop, and the current command is calculated by the PI regulator. The obtained current command value is then distributed to the input ends of each current loop through the excitation / armature current distribution module, thereby controlling the active power output by the system and maintaining the output voltage stable.

[0054] AC excitation HESG electromagnetic constraints such as Figure 2 As shown, the current limit is based on (0, 0) as the center, i smax The voltage limit is a circle with a radius of ((-ψ pms -L dm i df ) / L ds , 0) as the center, major axis a=u smax / ωL ds and the minor axis b=u smax / ωL qs Ellipse. Among them, u smax is the armature winding output voltage limit value, i smax is the current limit that the armature winding can withstand, and ω is the synchronous angular frequency of the motor.

[0055] According to the topological structure of AC excitation HESG and its magnetic regulation principle, its physical model in dq rotating coordinate system can be obtained, as shown in the following figure: Figure 3 shown. Figure 4 The comparison chart of experimental results is shown in Figure 2. Figure 4 (a) is a comparison chart of the variable speed voltage stabilization test results of controlling the excitation current alone. Figure 4 (b) is a comparison chart of the variable speed voltage stabilization experiment results of controlling the armature current alone. Figure 4 (c) is a comparison chart of the low-speed operation experimental results of current coordinated control. Figure 4 (d) is a comparison chart of the high-speed operation experimental results of current coordinated control. Figure 4 (e) is a comparison chart of copper consumption at different speeds.

[0056] The minimum copper loss coordinated control method of the permanent magnet motor system specifically includes the following steps:

[0057] Step 1: Based on the topological structure of the AC excitation HESG and its magnetic regulation principle, the physical model of the motor in the dq rotating coordinate system is obtained, and the voltage equation, magnetic flux equation, and electromagnetic torque equation in the dq coordinate system are derived.

[0058] In one embodiment, the above step 1 specifically includes:

[0059] To simplify the analysis, the AC-excited HESG is assumed to be an ideal motor, with the armature windings constructed as generators and the field windings as motors. The following rules apply: When positive current flows through the three-phase armature windings, positive flux is generated; when positive current flows through the three-phase field windings, positive flux is generated. The equations for voltage, flux, and electromagnetic torque in the dq coordinate system are as follows:

[0060] Voltage equation:

[0061]

[0062] Where, subscripts s and f represent the parameters of armature winding and excitation winding respectively; subscripts d and q represent the parameters of d-axis and q-axis respectively; ψ df , ψ qf Respectively represent the d-axis and q-axis magnetic flux of the excitation winding; ψ ds , ψ qs Represent the armature winding d-axis and q-axis magnetic flux respectively; i df 、i qf are the d-axis and q-axis components of the excitation current respectively; i ds 、i qs are the d-axis and q-axis components of the armature current respectively; u df 、u qf are the d-axis and q-axis components of the excitation voltage respectively; u ds 、u qs are the d-axis and q-axis components of the armature voltage respectively.

[0063] Magnetic flux equation:

[0064]

[0065] Electromagnetic torque equation:

[0066]

[0067] Where p is the differential operator; T em is the electromagnetic torque; ω is the synchronous angular frequency of the motor; R s , R f are the internal resistances of the armature winding and the field winding respectively; L ds , L qs , L df , L qf are the d-axis self-inductance and q-axis self-inductance of the armature winding and the d-axis self-inductance and q-axis self-inductance of the excitation winding respectively; L dm is the mutual inductance between the field winding and the armature winding d-axis; L qm is the mutual inductance between the excitation winding and the armature winding q axis; ψ pms and ψ pm are the permanent magnet flux amplitudes on the armature winding and the excitation winding respectively; n ps , npf are the number of pole pairs of the armature winding and the field winding respectively.

[0068] Step 2: Based on the magnetic adjustment and speed expansion requirements in the low-speed and high-speed operation stages, the Lagrangian equations under different constraint conditions were derived respectively.

[0069] In one example, step 2 specifically includes:

[0070] When the AC excitation HESG runs at high speed, the back electromotive force is large. Ignoring the resistance voltage drop, the armature winding dq axis voltage equation is:

[0071]

[0072] Due to the current limit of the excitation winding and the voltage and current limit of the rectifier itself, the voltage and current of the HESG should meet the following requirements:

[0073]

[0074] Where i fmax is the current limit value of the excitation winding.

[0075] In summary, the dq axis current constraints are obtained:

[0076]

[0077] Ignoring the switching loss of the PWM rectifier, the output electromagnetic power P of the AC excitation HESG is e and the total power consumed by the load P load It can be expressed as follows:

[0078]

[0079] Where U dc is the output DC voltage reference value; R is the DC load.

[0080] Furthermore, the DC bus voltage equation is:

[0081]

[0082] In order to prevent the permanent magnet from demagnetizing, the armature current magnetic component i is adjusted when the motor is running at low speed. ds Set to 0A. In addition, since the back EMF is small at low speeds and is not limited by the inverter voltage limit, the Lagrange equation at low speeds can be expressed as follows:

[0083]

[0084] Where λ is the Lagrange multiplier.

[0085] Taking the derivative of each variable in the above formula and setting it to 0, we get

[0086]

[0087] When the motor is running at high speed, the motor back electromotive force is high, and the inverter voltage limit needs to be considered. Therefore, the Lagrange equation at high speed is:

[0088]

[0089] Where λ1 and λ2 are Lagrange multipliers.

[0090] The Newton iteration method is used to solve the partial derivative equation, and the optimal solution of each variable is obtained as follows:

[0091]

[0092] Step 3: With the minimum copper loss of the motor as the optimization goal, the excitation and armature currents are distributed online to achieve coordinated control of the excitation and armature currents.

[0093] In one example, step 3 specifically includes:

[0094] The optimal distribution of excitation and armature currents is obtained with the goal of minimizing copper loss, and the Lagrange multiplier method is used to solve the optimal solution for each reference current. For minimum copper loss control, the objective function is:

[0095]

[0096] With the goal of minimizing copper loss, the optimal distribution of excitation current and armature current is obtained, and the Lagrange multiplier method is used to solve the optimal solution of each reference current.

[0097] Figure 4 The experimental comparison between the traditional AC excitation HESG control strategy and the coordinated control strategy is given. Figure 4 From (a) in the figure, we can see that the speed regulation range of the excitation current is 500r / min~850r / min. Figure 4 From (b) in the figure, we can see that the speed regulation range of the armature current is 300r / min to 1450r / min. Figure 4 From (c) in the figure, it can be seen that when the motor is running at low speed (240r / min~1300r / min), by adjusting the excitation current d-axis component idf and the armature current q-axis component i qs Ensure the output DC voltage is stable. Figure 4 From (d) in the figure, we can see that when the motor is running at high speed (1300r / min~1600r / min), the back electromotive force exceeds the DC bus voltage. In this stage, by adjusting the three current variables i ds 、iqs and i df It can be seen that the speed-variable voltage-stabilizing range of the coordinated control strategy is 240r / min to 1600r / min, which is 3.9 times higher than that of the traditional current control strategy, showing a significant advantage. Figure 4 As shown in (e) of Figure 1, the copper loss of the minimum copper loss control strategy is lower than that of the speed partition control strategy throughout the entire variable speed operating range, demonstrating the effectiveness of the proposed minimum copper loss coordinated control strategy. The above analysis demonstrates that the proposed method can achieve optimal distribution of excitation and armature currents.

[0098] The above merely describes a preferred embodiment of the present invention. A person skilled in the art will readily appreciate other advantages and variations based on the above embodiment. Therefore, the present invention is not limited to the above embodiment, which serves only as an example to provide a detailed, illustrative description of one form of the present invention. Any common changes and substitutions made by a person skilled in the art within the scope of the present invention's technical solution, without departing from the spirit of the present invention, should be included within the scope of protection of the present invention.

Claims

1. A method for minimum copper loss coordinated control of a permanent magnet motor system, characterized in that: The steps include: S1. Based on the topological structure of the AC-excited HESG and its magnetic regulation principle, the physical model of the motor in the dq rotating coordinate system is obtained, and the voltage equation, flux equation, and electromagnetic torque equation in the dq coordinate system are derived; S2, based on the magnetic adjustment and speed expansion requirements in low-speed and high-speed operation stages, derive the Lagrangian equations under different constraints; S3, with the minimum copper loss of the motor as the optimization goal, distributes the excitation current and armature current online to achieve coordinated control of the excitation current and armature current; Assuming that the AC excitation HESG is an ideal motor, when a positive current flows through the three-phase armature winding, a positive flux is generated. When a positive current flows through the three-phase excitation winding, a positive flux is generated. From this, the voltage equation, flux equation, and electromagnetic torque equation in the dq coordinate system can be obtained as follows: Voltage equation: Where, subscripts s and f represent the parameters of armature winding and excitation winding respectively; subscripts d and q represent the parameters of d-axis and q-axis respectively; ψ df , ψ qf Respectively represent the d-axis and q-axis magnetic flux of the excitation winding; ψ ds , ψ qs Represent the armature winding d-axis and q-axis magnetic flux respectively; i df 、i qf are the d-axis and q-axis components of the excitation current respectively; i ds 、i qs are the d-axis and q-axis components of the armature current respectively; u df 、u qf are the d-axis and q-axis components of the excitation voltage respectively; u ds 、u qs are the d-axis and q-axis components of the armature voltage respectively; Magnetic flux equation: Electromagnetic torque equation: Where p is the differential operator; T em is the electromagnetic torque; ω is the synchronous angular frequency of the motor; R s , R f are the internal resistances of the armature winding and the field winding respectively; L ds , L qs They are the armature winding d-axis self-inductance and q-axis self-inductance, L df , L qf are the d-axis self-inductance and q-axis self-inductance of the excitation winding respectively; L dm is the mutual inductance between the field winding and the armature winding d-axis; L qm is the mutual inductance between the excitation winding and the armature winding q axis; ψ pms and ψ pmf are the permanent magnet flux amplitudes on the armature winding and the excitation winding respectively; n ps , n pf are the pole pairs of the armature winding and the field winding respectively; In step S2: When the AC excitation HESG runs at high speed, the armature winding dq axis voltage equation is: And should meet the following requirements: Where i fmax is the current limit value of the excitation winding; The dq axis current constraints are obtained: Ignoring the switching loss of the PWM rectifier, the output electromagnetic power P of the AC excitation HESG is e and the total power consumed by the load P load It is expressed as follows: Furthermore, the DC bus voltage equation is: Among them, U dc is the output DC voltage reference value; R is the DC load; The Lagrange equation during high-speed operation is: Where λ1 and λ2 are Lagrange multipliers; In the low speed operation stage, the armature current magnetic component i ds Set to 0A, the Lagrange equation is expressed as follows: Where λ is the Lagrange multiplier.

2. The method for minimum copper loss coordinated control of a permanent magnet motor system according to claim 1, characterized in that: In step S3, the objective function of minimum copper loss control is: With the goal of minimizing copper loss, the optimal distribution of excitation current and armature current is obtained; the Lagrange multiplier method is used to solve the optimal solution of each reference current.

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