Auxiliary inverter control method and device under secondary pulse condition

Abstract

According to the auxiliary inverter control method under the secondary pulsation condition, the actual voltage value of a direct current bus is detected, a feedforward coefficient is calculated and obtained, the feedforward coefficient is multiplied by the output modulation ratio under voltage and current double closed loops, the modulation ratio is corrected, and therefore the influence of the secondary pulsation of the voltage of the direct current bus on the modulation process of the auxiliary inverter is eliminated, and the control accuracy of the auxiliary inverter is improved. And the output voltage THD and the three-phase unbalance degree of the auxiliary inverter are ensured to meet the requirements. After a passive LC resonant filter is cancelled, through voltage and current double-closed-loop control with direct-current bus voltage feedforward, the third harmonic component and the three-phase unbalance degree of output voltage of the auxiliary inverter under the rated load condition are reduced, stable operation of the auxiliary inverter under the secondary pulse condition is ensured, improvement is conducted through a software algorithm, and the stability of the auxiliary inverter is improved. The power density of the whole vehicle is improved, and equipment cost is reduced.

Description

Technical Field

[0001] The present invention relates to the field of rail transit power electronics technology, and in particular to an auxiliary inverter control method under secondary pulsation conditions. Background Art

[0002] When the high-speed train is powered by the overhead line, the single-phase four-quadrant converter will generate secondary pulsating power. This secondary pulsating power flows in the DC bus capacitor, which will cause the DC bus voltage to have obvious secondary pulsating components, affecting the power supply quality of the auxiliary converter. The prior art generally uses a passive LC resonant filter to decouple the secondary pulsating power so that it no longer flows in the DC bus capacitor, thereby ensuring the stability of the DC bus voltage. However, the passive LC resonant filter has the disadvantages of large size and weight, which reduces the power density of the traction converter and is not conducive to the lightweight development of the EMU. At the same time, the hardware filter belongs to the hardware solution, which has a certain equipment cost and reduces the overall reliability of the system. Summary of the invention

[0003] In a first aspect, the present invention provides a method for controlling an auxiliary inverter under secondary pulsation conditions, comprising the following steps:

[0004] Establish a mathematical model of the three-phase voltage value expected to be output;

[0005] Get the actual value of DC bus voltage;

[0006] Adjust the modulation ratio;

[0007] Set the feedforward coefficient. The value of the feedforward coefficient is equal to the DC bus voltage target value divided by the DC bus actual value.

[0008] The modulation wave in the three-phase stationary coordinate system is obtained through dq / abc transformation;

[0009] The feedforward coefficient is multiplied by the three-phase modulation wave respectively to correct the output modulation ratio.

[0010] Based on the above scheme, the mathematical model includes the expected output voltage values ​​of phase a, phase b, and phase c, which are respectively represented by u an ,u bn ,u cn :

[0011]

[0012]

[0013]

[0014] Where ω is the grid angular frequency, U dc is the DC bus voltage target value, Udc-ripple is the amplitude of the secondary pulsating voltage of the DC bus, and θ is the phase of the secondary pulsating voltage of the DC bus.

[0015] Based on the above scheme, the adjusted modulation ratio is expressed as:

[0016]

[0017] Based on the above scheme, the feedforward coefficient K udc It is expressed as:

[0018]

[0019] On the basis of the above scheme, the auxiliary inverter control of the EMU adopts a voltage and current dual closed-loop control in a rotating coordinate system, including a voltage outer loop and a current inner loop; the voltage outer loop obtains a current command value through a voltage controller; through the voltage outer loop, the voltage command value of the q-axis is set to 0; the current inner loop tracks the voltage outer loop to calculate the current command.

[0020] In the second aspect, any of the above-mentioned schemes is applied to provide an auxiliary inverter, wherein the front-end bridge arm is a single-phase four-quadrant converter bridge arm for converting AC power into DC power; the rear-end bridge arm is a three-phase inverter bridge arm for converting DC power into AC power; and the passive LC resonant circuit is cancelled on the intermediate DC side.

[0021] According to a third aspect, an electronic device is provided, comprising a memory and a processor, wherein the memory stores a computer program, and the processor implements the steps of any of the above methods when executing the computer program.

[0022] According to a fourth aspect, a computer-readable storage medium is provided, on which a computer program is stored, and when the computer program is executed by a processor, the steps of any of the above methods are implemented.

[0023] Beneficial effects of the present invention:

[0024] After eliminating the passive LC resonant filter, the present invention reduces the third harmonic component of the auxiliary inverter output voltage and the three-phase imbalance under rated load conditions through voltage and current dual closed-loop control with DC bus voltage feedforward, ensures the stable operation of the auxiliary inverter under secondary pulsation conditions, improves the power density of the entire vehicle through software algorithms, and reduces equipment costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention has the following accompanying drawings:

[0026] Figure 1 It is a physical picture of the LC secondary resonant branch of the prior art traction converter and a schematic diagram of its volume and weight;

[0027] Figure 2 This is a topological diagram of the auxiliary inverter circuit of the present invention;

[0028] Figure 3 A physical model of the auxiliary inverter of the present invention;

[0029] Figure 4 This is a schematic diagram of voltage and current dual closed-loop control of the present invention;

[0030] Figure 5 It is a schematic diagram of the modulation ratio correction of the feedforward coefficient of the present invention. DETAILED DESCRIPTION

[0031] To make the objects, advantages and features of the present invention more apparent, the following Figure 1-5 The present invention is further described in detail with reference to the following specific embodiments.

[0032] Usually, connecting an LC secondary resonant branch in parallel with the intermediate DC bus can decouple and absorb the AC component in the input power, fundamentally solving the secondary pulsation problem. Figure 1 As shown in the figure, a set of physical pictures of the LC secondary resonant branch of the traction converter and the corresponding volume and weight analysis are given. It can be seen that the passive LC secondary resonant branch has the disadvantage of large volume and weight, which reduces the power density and integration of the traction converter. Taking the 16-unit 8-motor 8-trailer train as an example, the whole vehicle needs to be equipped with 8 sets of LC secondary resonant branches, so they will occupy the volume of 716.8L and the weight of 1100.8kg of the EMU, which is not conducive to the efficient and economical operation of the EMU. At the same time, since the LC secondary resonant branch will flow through a large current, it will cause loss and heating problems, increasing the heat dissipation requirements of the system. As the service time of the EMU increases, the capacitance of the resonant decoupling capacitor will inevitably decay, resulting in the shift of the resonance point, reducing the passive decoupling performance and the reliability of the traction converter. In addition, as a passive hardware device, the LC secondary resonant branch will increase the initial equipment investment cost and the later operation and maintenance cost.

[0033] like Figure 2 The figure shows a specific embodiment of the auxiliary inverter circuit topology diagram of the present invention. The auxiliary inverter of the EMU obtains the DC voltage from the DC bus side, and obtains the three-phase output voltage after inversion by the three-phase inverter bridge, voltage transformation by the isolation transformer, and filtering by the filtering link, and supplies it to the medium voltage equipment of the EMU. The three-phase inverter is composed of 6 IGBTs, which are controlled by the control system; the power frequency isolation transformer adopts the connection form of Δ / yn-11; the secondary side of the transformer integrates the equivalent leakage inductance, which can be combined with the output filter capacitor to form an output filter circuit. In the figure: u A 、u B 、u C is the midpoint voltage of the three-phase bridge arm, u a 、ub 、u c is the transformer secondary phase voltage, L m is the equivalent leakage inductance integrated on the secondary side of the transformer, C f is the output filter capacitor, R m is the equivalent impedance of the line, u an 、u bn 、u cn is the output voltage of the auxiliary inverter, i an 、i bn 、i cn is the output current of the auxiliary inverter, i La 、i Lb 、i Lc is the secondary inductor current.

[0034] Assume that the output voltage of phase A is u an . Then u an The DC bus voltage u dc And modulation ratio m is expressed as:

[0035]

[0036] Where ω is the grid angular frequency.

[0037] When u dc When there is secondary pulsation in dc It can be expressed as:

[0038] u dc =U dc +U dc-ripple sin(2ωt+θ)

[0039] Among them, U dc is the DC bus voltage target value, U dc-ripple is the amplitude of the secondary pulsating voltage of the DC bus, and θ is the phase of the secondary pulsating voltage of the DC bus.

[0040] Assume Ucos(ωt) is the expected output voltage value of phase a, then u an It can be expressed as:

[0041]

[0042]

[0043] Similarly, the output voltages of the other two phases under DC secondary pulsation can be derived.

[0044] Assume Ucos(ωt-2π / 3) is the expected output voltage value of phase b, then u bn It can be expressed as:

[0045]

[0046]

[0047] Assume Ucos(ωt+2π / 3) is the expected output voltage value of phase c, then u cn It can be expressed as:

[0048]

[0049]

[0050] In addition to the fundamental component of the expected output, each phase output voltage also has additional fundamental components and third harmonic components superimposed. Since the hybrid electric vehicle power frequency transformer adopts the Δ / yn-11 connection form, the primary side is a triangle connection. This connection can prevent the third harmonic of the same phase in the primary side output PWM pulse voltage from entering the secondary side. However, when there is secondary pulsation in the DC bus voltage, there will be three-phase symmetrical third harmonics in the three-phase output voltage. The symmetrical third harmonics on the primary side will enter the secondary side through the transformer. Therefore, the auxiliary inverter output voltage contains third harmonics, and each phase will have additional fundamental components that will enter the secondary side, which will significantly increase the imbalance of the three-phase output voltage of the auxiliary inverter.

[0051] Since the actual value of the DC bus voltage u dc The existence of secondary pulsating voltage increases the imbalance of the three-phase output voltage, so the modulation ratio can be corrected by adjusting the actual value of the DC bus voltage u dc Sampling, calculate the feedforward coefficient K of the modified modulation ratio udc , thus achieving the effect of feedforward compensation.

[0052] The modulation ratio m can be adjusted as follows:

[0053]

[0054] Feedforward coefficient K udc It can be expressed as:

[0055]

[0056] like Figure 3 and Figure 4 As shown in the figure, the auxiliary inverter control of the EMU adopts voltage and current dual closed-loop control in a rotating coordinate system, including a voltage outer loop and a current inner loop. The voltage outer loop has two functions: one is to obtain the current command value through the voltage controller, and the other is to set the voltage command value of the q axis to 0 through the voltage outer loop to achieve the effect of unity power factor and stabilize the output voltage amplitude. The main function of the current inner loop is to track the current command calculated by the voltage outer loop to achieve rapid current tracking.

[0057] like Figure 5 As shown, when the dual closed-loop control output is transformed through dq / abc to obtain a modulation wave in a three-phase stationary coordinate system, the feedforward coefficient is multiplied by the three-phase modulation wave to correct the output modulation ratio, thereby realizing the optimal control of the auxiliary inverter under secondary pulsation.

[0058] The above implementation modes are only used to illustrate the present invention, but not to limit the present invention. Ordinary technicians in the relevant technical field can make various changes and modifications without departing from the essence and scope of the present invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention, and the patent protection scope of the present invention should be defined by the claims. The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in this field.

Claims

1. A method for controlling an auxiliary inverter under secondary pulsation conditions, characterized in that: The steps include: Establish a mathematical model of the three-phase voltage value expected to be output; Get the actual value of DC bus voltage; Adjust the modulation ratio; Set the feedforward coefficient. The value of the feedforward coefficient is equal to the DC bus voltage target value divided by the DC bus actual value. The modulation wave in the three-phase stationary coordinate system is obtained through dq / abc transformation; The feedforward coefficient is multiplied by the three-phase modulation wave respectively to correct the output modulation ratio.

2. The auxiliary inverter control method under secondary pulsation condition according to claim 1, characterized in that: The mathematical model includes the expected output voltage values ​​of phase a, phase b, and phase c, which are respectively represented by u an ,u bn ,u cn : Where ω is the grid angular frequency, U dc is the DC bus voltage target value, U dc-ripple is the amplitude of the secondary pulsating voltage of the DC bus, and θ is the phase of the secondary pulsating voltage of the DC bus.

3. The auxiliary inverter control method under secondary pulsation condition as claimed in claim 2, characterized in that: The adjusted modulation ratio is expressed as:

4. The auxiliary inverter control method under secondary pulsation condition as claimed in claim 2, characterized in that: The feedforward coefficient K udc It is expressed as:

5. The auxiliary inverter control method under secondary pulsation condition according to claim 1, characterized in that: The auxiliary inverter control of the EMU adopts voltage and current double closed-loop control in a rotating coordinate system, including a voltage outer loop and a current inner loop; the voltage outer loop obtains a current command value through a voltage controller; The voltage command value of the q-axis is set to 0 through the voltage outer loop; and the current inner loop tracks the voltage outer loop to calculate the current command.

6. An auxiliary inverter, wherein the front bridge arm is a single-phase four-quadrant converter bridge arm for converting AC power into DC power; the rear bridge arm is a three-phase inverter bridge arm for converting DC power into AC power; characterized in that: A method for controlling an auxiliary inverter under secondary pulsation conditions as claimed in any of claims 1 to 5 is applied.

7. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, the steps of the auxiliary inverter control method under secondary pulsation conditions described in any one of claims 1 to 5 are implemented.

8. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of a method for controlling an auxiliary inverter under secondary pulsation conditions according to any one of claims 1 to 5 are implemented.

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