Method for improving power factor of synchronous reluctance motor based on suspension capacitor topology

Abstract

The application discloses a synchronous reluctance motor power factor improvement method based on a suspension capacitor topology, and comprises the following steps: obtaining a synchronous reluctance motor, adopting different current distribution schemes for the synchronous reluctance motor; obtaining a current angle change amount based on the current distribution scheme, and obtaining a real-time power factor of the synchronous reluctance motor based on the current angle change amount; and performing current angle adjustment and variable capacitor voltage adjustment control on the synchronous reluctance motor based on the real-time power factor. The open-loop reactive power compensation control and the open-loop variable capacitor voltage control are simple and practical, are easy to calculate, are close to the effect of the closed-loop reactive power compensation, can reduce the use of the controller, and reduce the dependence on PI parameters.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of multiphase motor drive control, and particularly relates to a synchronous reluctance motor power factor improvement method based on a suspension capacitor topology. BACKGROUND

[0002] A synchronous reluctance motor SynRM (Synchronous Reluctance Motor), also known as a reluctance synchronous motor, has the same stator structure as an asynchronous motor and a salient pole structure. The SynRM generates an electromagnetic torque according to the principle of minimum magnetic resistance and generates an electromagnetic torque by using the uneven magnetic resistance of the rotor. The SynRM has low manufacturing cost, simple control mode, high temperature resistance and other advantages, and has broad application prospects. However, due to the low power factor, the application of the SynRM is limited.

[0003] Many studies try to improve the performance of the SynRM in structure, such as using different magnetic barrier geometries, magnetic materials, stator winding types, etc. In terms of improving the power factor, researchers improve the salient pole ratio by designing and optimizing new rotor structures. However, it is difficult to manufacture a SynRM with a high salient pole ratio and it is accompanied by an increase in cost. In the field of motor control, a maximum power factor control strategy (MPFC) is proposed, which can improve the power factor of the SynRM. However, compared with the maximum torque current ratio control strategy (MTPA), this control strategy increases the stator current to generate the same torque, which increases the copper loss and reduces the efficiency. SUMMARY

[0004] The purpose of the present application is to provide a synchronous reluctance motor power factor improvement method based on a suspension capacitor topology to solve the problems existing in the prior art.

[0005] To achieve the above purpose, the present application provides a synchronous reluctance motor power factor improvement method based on a suspension capacitor topology, comprising the following steps:

[0006] Obtain a synchronous reluctance motor, and adopt different current distribution schemes for the synchronous reluctance motor;

[0007] Obtain a current angle change based on the current distribution scheme, and obtain a real-time power factor of the synchronous reluctance motor based on the current angle change;

[0008] Adjust the current angle and control the variable capacitor voltage of the synchronous reluctance motor based on the real-time power factor.

[0009] Optionally, the process of adopting different current distribution schemes for the synchronous reluctance motor comprises:

[0010] calculating a power factor of the synchronous reluctance motor;

[0011] calculating an electromagnetic torque of the synchronous reluctance motor;

[0012] adopting different current distribution schemes for the synchronous reluctance motor based on the power factor and the electromagnetic torque.

[0013] Optionally, the process of calculating a power factor of the synchronous reluctance motor comprises:

[0014] Neglecting the effect of stator resistance, the power factor equation of the synchronous reluctance motor can be simplified as:

[0015]

[0016] wherein the salient pole ratio of the motor K = L d / L q , x = sin 2 γ.

[0017] Optionally, the process of calculating an electromagnetic torque of the synchronous reluctance motor comprises:

[0018] Neglecting the effect of magnetic saturation on inductance, the electromagnetic torque equation of the synchronous reluctance motor is:

[0019]

[0020] wherein L d , L q is fixed.

[0021] Optionally, the process of obtaining a current angle change amount based on the current distribution scheme comprises:

[0022] Based on the current distribution scheme, different current angles are selected for current distribution and are taken as reference currents of the current inner loop.

[0023] Optionally, the process of performing variable-capacitance voltage regulation control on the synchronous reluctance motor based on the real-time power factor comprises:

[0024] Obtaining an average power factor of the synchronous reluctance motor, and setting a minimum power factor value based on the average power factor;

[0025] When the real-time power factor is lower than the minimum power factor value, adjusting the current angle of the synchronous reluctance motor.

[0026] Optionally, the process of performing variable-capacitance voltage regulation control on the synchronous reluctance motor based on the real-time power factor further comprises:

[0027] Constructing a voltage current vector relationship of the synchronous reluctance motor, calculating a voltage vector that the synchronous reluctance motor needs to compensate based on the voltage current vector relationship;

[0028] Obtaining a reference voltage based on the voltage vector that the synchronous reluctance motor needs to compensate;

[0029] Obtaining a suspension capacitor voltage of the synchronous reluctance motor, and calculating a reference value of the reference voltage and the suspension capacitor voltage;

[0030] Based on the reference value, the synchronous reluctance motor is subjected to variable capacitor voltage adjustment control.

[0031] The technical effects of the present application are:

[0032] The open-loop reactive compensation control and the open-loop variable capacitor voltage control provided by the present application are simple and practical, easy to calculate, close to the effect of closed-loop reactive compensation, can reduce the use of controllers, and reduce the dependence on PI parameters. Compared with the single control scheme of SynRM, the segmented control strategy provided by the present application is more suitable for the characteristics of SynRM, and improves the power factor in the high-speed interval. BRIEF DESCRIPTION OF DRAWINGS

[0033] The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application and are incorporated in and constitute a part of this application. The embodiments of the present application illustrated in the drawings and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0034] Figure 1 is a voltage current vector relationship diagram provided by the present application;

[0035] Figure 2 is a power factor waveform diagram of SynRM using the segmented control strategy switching provided by the present application;

[0036] Figure 3 is a power factor waveform diagram of SynRM using only the traditional maximum torque current ratio control;

[0037] Figure 4 is a power factor waveform diagram of the power supply side inverter using the open-loop compensation strategy provided by the present application;

[0038] Figure 5 is a power factor waveform diagram of the power supply side inverter using the closed-loop control compensation strategy;

[0039] Figure 6 is a comparison waveform diagram of the suspension capacitor measurement inverter modulation ratio of the variable capacitor voltage control and the fixed capacitor voltage control used by the present application;

[0040] Figure 7This is a flow chart of the method for improving the power factor of a synchronous reluctance motor based on a suspended capacitor topology according to the present invention. DETAILED DESCRIPTION

[0041] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0042] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0043] Example 1

[0044] like Figures 1-7 As shown, this embodiment provides a method for improving the power factor of a synchronous reluctance motor based on a suspended capacitor topology. Based on a six-phase open-winding topology with a suspended capacitor hybrid power supply, the present invention adopts an optimal control scheme to improve the SynRM power factor at different motor speeds. The reactive voltage vector that needs to be compensated is calculated based on changes in the current angle and power factor angle, and is provided by the suspended capacitor side, aiming to solve the problem of low power factor in the SynRM.

[0045] This embodiment discusses the optimal solution at different speeds. When the SynRM is running at low speed, if the maximum power factor control strategy is adopted, the current angle is large, such as 65-85° under the common salient pole ratio. At this time, the stator current required to produce the same electromagnetic torque is greater than that using the maximum torque current ratio control, resulting in increased copper loss. At the same time, due to the low motor speed, the motor power factor is large, close to 0.7, and the maximum torque current ratio control strategy is suitable at this time. When the SynRM is running at high speed, the output power of the SynRM increases and gradually reaches the rated power of the motor. At the same time, as the speed increases, the motor's demand for reactive power increases. At this time, it is necessary to reduce reactive power, thereby reducing reactive loss, so it is more appropriate to adopt the maximum power factor control strategy.

[0046] After changing the motor's current angle, the system's power factor improves. The voltage vector required for compensation can be calculated based on the real-time power factor value. This is then combined with the voltage vector maintaining the floating capacitor voltage to form the reference voltage vector on the floating capacitor inverter side. The reactive power required by the motor is provided by the floating capacitor inverter. As the demand for reactive power increases, the floating capacitor inverter may become insufficiently compensated, necessitating an increase in the floating capacitor inverter's voltage. Therefore, voltage control of the variable capacitor on the floating capacitor inverter side is also necessary.

[0047] The application proposes a scheme of adopting maximum torque current ratio control when the SynRM is at low rotating speed (high power factor) and adopting maximum power factor control when the SynRM is at high rotating speed (low power factor), and selecting a control strategy switching point according to the specific power factor drop of the motor. According to the change of the current angle and the change of the power factor, the reactive voltage vector needing compensation is calculated, and the suspension capacitor voltage reference value is obtained, so as to realize variable capacitor voltage control. The suspension capacitor side inverter provides reactive power, improves the utilization rate of the power supply voltage, and prevents the power factor from dropping due to insufficient power supply voltage vector at high speed. The two control strategies are combined to comprehensively improve the power factor of the SynRM.

[0048] The application provides a method of adopting segmented control current angle to improve the power factor of the SynRM, and calculates the voltage vector of reactive power compensation. The whole process considers the power factor optimization and simplifies the reactive power compensation process.

[0049] For the vector control scheme of the motor, the power factor equation of the SynRM can be simplified as:

[0050]

[0051] Wherein the salient pole ratio K of the motor is defined as L d / L q , x=sin 2 γ, it can be seen that the power factor of the motor is only determined by the current angle γ. Derivation of x can know that when the current angle γ=90°, the power factor of the motor reaches the maximum.

[0052] Similarly, ignoring the influence of magnetic saturation on inductance, L d , L q is fixed, the torque equation of the SynRM is:

[0053]

[0054] For the same current amplitude, the electromagnetic torque is only determined by the current angle γ. The electromagnetic torque T e is derived with respect to the current angle γ, and it can be known that when the current angle γ=45°, the motor realizes unit current maximum torque.

[0055] Therefore, for different control purposes, different current distribution schemes need to be adopted for the stator current. When the distribution scheme of γ=45° is adopted, it is maximum torque current ratio control; when γ=0°, it is maximum power factor control. In the application, the current vector I s *According to different motor control strategies, different current angles γ are selected to distribute the current to the d and q axes as the reference current i of the current inner loop d * 、 q * .

[0056]

[0057] Since the power factor of the SynRM will decrease as the speed of the motor increases, in order to stabilize the power factor of the motor at a high level, the application proposes to set a minimum power factor value for the control system. When the value is lower than this value, the control strategy is switched from the maximum torque current ratio control to the maximum power factor control. The specific determination point is that the average value of the power factor of the motor at low speed and in a steady state is preliminarily determined and set as the determination value, the power factor of the motor is measured in the process of accelerating the motor, and it is defined as PF * When the value of PF * is lower than 90% of the initial power factor value of the motor, the current angle γ of the maximum power factor control is switched to As in the embodiment of the application, the average value of the power factor is about 0.7 when the motor is at low speed and uses the maximum torque current ratio control, and when the power factor of the motor decreases to 0.63 or below, which is 90% of the power factor, the current angle γ is switched, and γ = 45° is switched to γ = 68°. The specific power factor at which the switching starts can be adjusted according to the actual situation.

[0058] Figure 1 is the relationship between the voltage and current vectors, wherein, U p is the active voltage component required by the system, U q is the reactive voltage component required by the system, I s is the current vector of the system, γ is the included angle between the current vector and the d axis (current angle), is the power factor angle. When the system is stable, U s and the power factor angle are constant, U s is output by the current loop PI controller, and U d and U q are synthesized, and the power factor angle φ is obtained from the phase difference between U s and I s . In order to realize that the reactive voltage component is completely provided by the suspension capacitor side inverter, the voltage vector U q required by the motor to be compensated can be calculated as follows:

[0059]

[0060] The suspension capacitor voltage control scheme is to send the error between the measured value of the capacitor voltage and the given value into a PI regulator to obtain a suspension capacitor charging voltage given value U p , to maintain the stability of the suspension capacitor voltage, it should be noted that: U p has positive and negative, determined by the charging and discharging state of the suspension capacitor. U q and U p The reference voltage vector U CI of the suspension capacitor inverter is synthesized.

[0061] The d, q axis reference voltage of the suspension capacitor inverter is:

[0062]

[0063] Variable capacitor voltage regulation: since U p is used to maintain the size of the suspension capacitor voltage, after charging U p is a very small amount, the voltage vector U CI of the suspension capacitor is mainly composed of the reactive compensation voltage vector U q . The modulation ratio of the suspension capacitor inverter is defined as:

[0064]

[0065] Where U cap is the voltage of the suspension capacitor, in order to improve the utilization rate of the reactive output capacity, the modulation ratio should be as high as possible, close to 1. Therefore, in the present application, the suspension capacitor voltage reference value is set as:

[0066] U cap * = 3.1U q (7)

[0067] The variable capacitor voltage control is realized by setting the reference voltage in open loop, and the theoretical modulation ratio in steady state is about 0.9. After considering the modulation, the theoretical modulation ratio can be increased according to the specific situation. The purpose of variable capacitor voltage regulation is to reduce the voltage of the suspension capacitor and improve the voltage utilization rate when the reactive power compensation demand is low, and to increase the voltage of the suspension capacitor and improve the reactive power compensation capacity when the reactive power compensation demand is high, further improving the power factor of the SynRM at high speed.

[0068] To verify the effectiveness of the above method, simulation verification is carried out on a six-phase open-winding SynRM. The six-phase open-winding SynRM is an open-winding motor, without considering the changes in motor parameters caused by magnetic saturation, hysteresis and eddy current. The parameters of the motor are shown in Table 1. Among them, R is the stator resistance, L d is the direct axis inductance, L q is the cross axis inductance, L ls is the stator leakage inductance, pn is the number of magnetic pole pairs. The DC bus voltage of the power inverter is 570 V, and the preset capacitor voltage of the suspension capacitor side inverter is 570 V.

[0069] Table 1

[0070] [[ L d ]]> L q ]]> R [[ L ls ]]> p n ]]> 0.09H 0.015H 1.4 Ω 0.001H 2

[0071] The six-phase open-winding SynRM speed command is set to 0.3 s at the start, and the speed is zero at this time. The power side inverter injects active power into the floating capacitor side inverter, and the suspension capacitor is pre-charged to 570 V. After 0.3 s, the capacitor is charged to the specified stable voltage. After 0.3 s, the speed command is changed to 500 r / min, and the speed is increased to 1000 r / min at 0.6 s. After the speed is stabilized, the speed is increased to the rated speed of 1500 r / min at 1.2 s, and a constant load of 4 N is applied after 0.3 s. According to the real-time power factor value, the current angle γ is automatically switched, and the control is changed from the maximum torque current ratio control to the maximum power factor control.

[0072] As shown in Figure 2 and Figure 3 , only the traditional maximum torque current ratio control and the power factor waveform of the SynRM using the segmented control strategy are compared. It can be seen that after the motor speed increases, the power factor decreases from 0.66 to 0.62. Since the determination point of the power factor is 0.63, after 1.2 s, the control strategy changes. Figure 2 In the control strategy, the power factor remains at about 0.66 before and after 1.2 s. The control strategy can effectively ensure that the motor power factor is in a high state.

[0073] As shown in Figure 4 and Figure 5 , compared with the open-loop reactive power compensation strategy, the power factor waveform of the power side inverter can be seen: in the steady state, the open-loop reactive power compensation to the unit power factor is a little worse than the closed-loop control, and at high speed, it can only be compensated to 0.987, which is only 0.05 different from the closed-loop control, which is not much different, but it is more stable in the steady state. In the working condition where the unit power factor compensation accuracy is not high, the open-loop reactive power compensation strategy can be used instead of the closed-loop reactive power compensation strategy, so that the system is simpler, easier to debug, and has lower control cost.

[0074] As shown in Figure 6 , the variable capacitor voltage control used in the present application is compared with the modulation ratio of the suspension capacitor measurement inverter under the constant capacitor voltage control. The first half is the modulation ratio under the variable capacitor voltage, which is close to 0.8 in the steady state, higher than the modulation ratio 0.15 under the constant capacitor voltage. This means that the utilization rate of the reactive power output capacity of the suspension capacitor inverter is higher under this control scheme.

[0075] From the simulation results above, it can be seen that the control method combining the segmented control strategy with a unit power factor control strategy has good effectiveness, and a flowchart of the method of the embodiment is as shown in Figure 7 .

[0076] The above merely provides the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, and any changes or replacements easily conceived by those skilled in the art within the technical scope disclosed by the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for power factor improvement of a synchronous reluctance motor based on a band suspended capacitor topology, characterized by, The method comprises the following steps: obtaining a synchronous reluctance motor, and adopting different current distribution schemes for the synchronous reluctance motor; obtaining a current angle change amount based on the current distribution scheme, and obtaining a real-time power factor of the synchronous reluctance motor based on the current angle change amount; performing current angle adjustment and variable-capacitance voltage adjustment control on the synchronous reluctance motor based on the real-time power factor; the process of performing current angle adjustment comprises: obtaining an average power factor of the synchronous reluctance motor, setting a minimum power factor value based on the average power factor, and adjusting the current angle of the synchronous reluctance motor when the real-time power factor is lower than the minimum power factor value; the process of performing variable-capacitance voltage adjustment control comprises: constructing a voltage-current vector relationship of the synchronous reluctance motor, calculating a voltage vector that needs to be compensated for the synchronous reluctance motor based on the voltage-current vector relationship, obtaining a reference voltage based on the voltage vector that needs to be compensated for the synchronous reluctance motor, obtaining a suspension capacitance voltage of the synchronous reluctance motor, calculating a reference value of the reference voltage and the suspension capacitance voltage, and performing variable-capacitance voltage adjustment control on the synchronous reluctance motor based on the reference value; the reference voltage vector of the suspension capacitance measurement inverter in the process of variable-capacitance voltage adjustment control is: The modulation ratio of the floating capacitor inverter is set as: wherein U CId , U CIq are the d-axis reference voltage, the p-axis reference voltage, respectively, U p is the active voltage component required by the system, U q is the reactive voltage component required by the system, γ is the angle between the current vector and the d-axis, m2 is the modulation ratio, U CI is the voltage vector of the inverter, U q is the voltage vector of the inverter, U p is the resultant voltage vector of the inverter, U cap is the voltage of the suspension capacitor.

2. The method for power factor improvement of synchronous reluctance motor based on band suspension capacitor topology according to claim 1, characterized in that, the process of adopting different current distribution schemes for the synchronous reluctance motor comprises: calculating a power factor of the synchronous reluctance motor; calculating an electromagnetic torque of the synchronous reluctance motor; adopting different current distribution schemes for the synchronous reluctance motor based on the power factor and the electromagnetic torque.

3. The power factor improvement method for synchronous reluctance motor based on band suspended capacitor topology according to claim 2, characterized in that, the process of calculating the power factor of the synchronous reluctance motor comprises: ignoring the influence of the stator resistance, and simplifying the power factor equation of the synchronous reluctance motor as: Wherein, the convex pole ratio K of the motor = L d / L q , x = sin 2 γ.

4. The method for improving the power factor of a synchronous reluctance motor based on a suspended capacitor topology according to claim 2, characterized in that: the process of calculating the electromagnetic torque of the synchronous reluctance motor comprises: ignoring the influence of magnetic saturation on inductance, and the electromagnetic torque equation of the synchronous reluctance motor is: wherein L d , L q is fixed.

5. The method for power factor improvement of synchronous reluctance motor based on band suspension capacitor topology according to claim 1, characterized in that, the process of obtaining a current angle change amount based on the current distribution scheme comprises: based on the current distribution scheme, selecting different current angles for current distribution, and taking the current angles as the reference current of the current inner loop.

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