Urban rail transit braking energy optimization method

Abstract

The invention relates to an urban rail transit braking energy optimization method, and belongs to the technical field of motor control through current. The method comprises the following steps: firstly, establishing a motor feedback energy Eback expression, and deriving the motor feedback energy Eback expression to obtain an expression of reference quadrature-axis current iq when Eback is maximum; when the motor starts braking, reading the maximum motor speed before braking of the motor, and obtaining a reference quadrature-axis current value according to the expression of the reference quadrature-axis current iq; and finally, setting a given quadrature-axis current value of a current loop in the motor to be the same as the reference quadrature-axis current # imgabs0 #, and setting a given direct-axis current value of the current loop to be 0. Compared with a traditional method in which the given quadrature-axis current output by a speed loop is directly used as the given quadrature-axis current of a current loop, the method has the advantages that the optimized reference quadrature-axis current value is obtained through a specific expression, and the feedback energy and the feedback efficiency during rail transit braking are greatly improved.

Description

Technical Field

[0001] The present invention relates to an optimization method for braking energy of urban rail transit, belonging to the technical field of controlling motors by current (H02P21 / 22). Background Art

[0002] With the accelerating urbanization process, modern urban rail transit has become a key path to solve the problem of traffic congestion. Nowadays, urban rail transit generally uses a flux-switching permanent magnet linear motor for driving. The advantage is that when the train brakes, the motor can absorb mechanical energy and convert it into electrical energy to be fed back to the power grid, greatly improving the energy utilization rate.

[0003] Currently, the traditional braking method is to set the given direct-axis current in the current loop of the motor to 0 when the train brakes, and directly use the given quadrature-axis current output by the speed loop as the given quadrature-axis current of the current loop. However, under this braking method, the feedback energy and feedback efficiency of the motor are relatively low, which not only causes energy waste, but also in the working condition where the subway needs to start and stop frequently, the low feedback efficiency will cause the voltage of the traction network of the subway system to rise, seriously threatening the safe and stable operation of the track traffic. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: how to improve the feedback energy and feedback efficiency during rail transit braking.

[0005] The technical solution proposed by the present invention to solve the above technical problem is: an optimization method for braking energy of urban rail transit, including the following steps: Step 1: Establish the expression of the motor feedback energy E shown in the following formula (1) back Expression (1); In formula (1), m is the mass of the motor; is the maximum motor speed before motor braking; is the motor speed after motor braking is completed; F e is the electromagnetic thrust; is the motor load force; R is the motor resistance; i q is the reference quadrature-axis current; is the ratio coefficient; is the stator pole pitch of the motor; is the permanent magnet flux linkage; Derive formula (1) to obtain the expression of the reference quadrature-axis current i when E back is maximum q Expression (2); Step 2: When the motor starts to brake, read the maximum motor speed before motor braking , calculate the reference quadrature-axis current \(i\) according to Equation (2) q ; Step 3: Set the given quadrature-axis current value of the current loop in the motor to the same magnitude as the reference quadrature-axis current , and set the given direct-axis current value of the current loop to 0.

[0006] Furthermore, in Step 2, it is determined whether the motor starts braking through the following Equation (3) (3); In Equation (3), \(P\) is the motor power; \(i_q\) is the real-time quadrature-axis current of the motor; \(i_d\) is the real-time direct-axis current of the motor; \(\omega\) is the real-time speed of the motor; When \(P \lt 0\), it is determined that the motor starts braking.

[0007] Furthermore, the real-time quadrature-axis current of the motor and the real-time direct-axis current of the motor are calculated through the following Equation (4) (4); In Equation (4), \(i_a\), a \(i_b\), b \(i_c\) c are the real-time three-phase currents of the motor; \(\theta\) is the real-time electrical angle of the motor.

[0008] The beneficial effects of the present invention are as follows: By obtaining a reasonable reference quadrature-axis current value through a specific expression and assigning it to the given quadrature-axis current of the current loop, instead of directly using the given quadrature-axis current output by the speed loop as the given quadrature-axis current of the current loop, the current loop can break through the static instruction limit of the speed loop output and match the optimal braking torque demand in real time. When the motor brakes, the optimized given quadrature-axis current value effectively improves the feedback energy and feedback efficiency of the motor, ensuring the safe and stable operation of the rail transit system. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The following further describes a method for optimizing braking energy of an urban rail transit according to the present invention with reference to the drawings.

[0010] Figure 1 is a waveform diagram of the change in the DC-side capacitor voltage caused by the feedback energy during motor braking in the traditional braking method.

[0011] Figure 2 is a waveform diagram of the change in the DC-side capacitor voltage caused by the feedback energy during motor braking in the braking energy optimization method of the urban rail transit in the embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS Embodiment

[0012] The urban rail transit braking energy optimization method of this embodiment includes the following steps: Step 1: Establish the expression of the motor feedback energy E shown in the following formula (1) back Expression (1); In formula (1), m is the mass of the motor; is the maximum motor speed before motor braking; is the motor speed after motor braking is completed; F e is the electromagnetic thrust; is the motor load force; R is the motor resistance; i q is the reference quadrature-axis current; is the ratio coefficient; is the motor stator pole pitch; is the permanent magnet flux linkage; Take the derivative of formula (1) to obtain the expression of the reference quadrature-axis current i when E back is the maximum q Expression (2).

[0013] When the motor starts to brake, read the maximum motor speed before motor braking, and calculate the reference quadrature-axis current i according to formula (2) q .

[0014] In this embodiment, it is judged that the motor starts to brake through the following formula (3) (3); In formula (3), P is the motor power; is the real-time quadrature-axis current of the motor; is the real-time direct-axis current of the motor; is the real-time speed of the motor; When P < 0, it is determined that the motor starts to brake; And the real-time quadrature-axis current of the motor and the real-time direct-axis current of the motor are calculated through the following formula (4) (4); In formula (4), i a , i b , i c are the real-time three-phase currents of the motor; θ is the real-time electrical angle of the motor.

[0015] In this embodiment, when the real-time three-phase current i a = -4.718A, i b = 2.995A, i c= 1.723 A, and when the real-time electrical angle θ = 260.58°, the real-time quadrature-axis current of the motor is calculated according to Equation (4) = -4.775 A, the real-time direct-axis current of the motor = -0.0288 A; at this time, the real-time speed of the motor = 0.5 m / s, combined with the motor resistance R = 0.16 Ω and substituted into Equation (3) to obtain P < 0, determining that the motor starts braking; Since the maximum motor speed before braking read = 1.75 m / s, = 0 m / s, the motor mass m = 6.2 kg, the motor load force = 5 N, the stator pole pitch of the motor = 48.7857 mm, the permanent magnet flux linkage = 0.01819 Wb, therefore, according to Equation (2), the reference quadrature-axis current i q = -4.7818 A.

[0016] Step 3: Set the given quadrature-axis current value in the current loop of the motor to the same magnitude as the reference quadrature-axis current, and set the given direct-axis current value of the current loop to 0.

[0017] In the motor control system, when the given quadrature-axis current value of the current loop is set, the proportional-integral controller (PI controller) therein will automatically adjust the duty ratio of the inverter dynamically according to the difference between the given quadrature-axis current value and the real-time quadrature-axis current value when the motor starts braking, and the difference between the given direct-axis current value and the real-time direct-axis current value when the motor starts braking, so as to eliminate the error between the real-time quadrature-direct-axis current value and the given quadrature-direct-axis current value, forcing the real-time quadrature-direct-axis current value to track the given quadrature-direct-axis current value.

[0018] As Figure 1 shown, in the traditional braking method, the capacitor voltage rises from 37 V to 65.8 V. Through the existing capacitor energy storage formula and the motor braking feedback efficiency formula, it is obtained that the capacitor increases by 4.44 J of feedback energy after braking, and the feedback efficiency is 51%; as Figure 2 shown, in this embodiment, the capacitor voltage rises from 37 V to 74.7 V. Through the existing capacitor energy storage formula and the motor braking feedback efficiency formula, it is obtained that the capacitor increases by 6.31 J of feedback energy after braking, and the feedback efficiency is 72.6%. Experimental data shows that the urban rail transit braking energy optimization method of this embodiment effectively improves the feedback energy and feedback efficiency during rail transit braking, which is beneficial to the recycling of resources and the stable operation of the rail transit system.

[0019] The above are only the preferred embodiments of the present invention, but the present invention is not limited thereto. All equivalent substitutions or equivalent changes made according to the concept and technical solution of the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for optimizing braking energy of urban rail transit, characterized in that The following steps are involved: Step 1: Establish the motor feedback energy E shown in the following equation (1): back expression （1）； In formula (1), m is the motor mass; is the maximum motor speed before motor braking; is the motor speed after motor braking is completed; F e It is electromagnetic thrust; is the motor load; R is the motor resistance; i q is the reference quadrature-axis current; is the ratio coefficient; is the motor stator pole pitch; is the permanent magnetic flux linkage; By taking the derivative of equation (1), we can get the following equation (2): back Maximum reference quadrature axis current i q The expression （2）； Step 2: When the motor starts to brake, read the maximum motor speed before the motor brakes , calculate the reference quadrature axis current i according to formula (2) q ; Step 3: Set the given quadrature-axis current value of the current loop in the motor to the same value as the reference quadrature-axis current The same size, the given direct axis current value of the current loop is set to 0.

2. The urban rail transit braking energy optimization method according to claim 1, characterized in that: The step 2 determines the start of motor braking by the following formula (3) （3）； In formula (3), P is the motor power; is the real-time quadrature-axis current of the motor; is the real-time direct-axis current of the motor; is the real-time speed of the motor; When P < 0, it is determined that the motor starts braking.

3. The urban rail transit braking energy optimization method according to claim 2, characterized in that: The real-time quadrature axis current of the motor and the real-time direct-axis current of the motor It can be calculated by the following formula (4): （4）； In formula (4), i a 、i b 、i c is the real-time three-phase current of the motor; θ is the real-time electrical angle of the motor.

Images