Bridge arm current optimization method for modular multi-level railway power regulator

Abstract

The invention discloses a modular multi-level railway power regulator bridge arm current optimization method. The method comprises the following steps: calculating modular multi-level railway power regulator bridge arm current stress data; setting a zero-sequence injection component based on the bridge arm current stress data, and optimizing the zero-sequence injection component to obtain an optimal zero-sequence injection component; and injecting the optimal zero-sequence injection component into a modulation signal, performing current stress optimization control, and outputting a pulse signal. According to the invention, no extra hardware circuit needs to be added, the reactive power of the traction power supply system can be compensated, the negative sequence component can be suppressed, the current stress distribution of the bridge arm is optimized, the phase unit loss of the device and the temperature fluctuation are reduced, and the reliability of the system is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of power regulators for power electronic traction power supply systems, relates to a bridge arm current optimization technology, and specifically relates to a modular multi-level railway power regulator bridge arm current optimization method. Background Art

[0002] Single-phase traction power supply systems are widely used in electrified railways, but their specific power supply system has reactive power and negative sequence problems, which will have an adverse effect on the three-phase power system. Among them, reactive power will increase the loss of lines and equipment and reduce the power factor of the power supply system; negative sequence current will destroy the symmetry of the three-phase power grid, which will then cause overheating and increased vibration of power grid equipment, seriously affecting the stable operation of the system. In addition, negative sequence components will also cause power quality problems, affecting the normal power consumption of other nearby users. Therefore, reactive power compensation and negative sequence suppression are crucial to ensure the safety of the traction power supply system and improve power supply efficiency.

[0003] In order to adapt to the voltage and power quality requirements of the medium-voltage traction network, modular multi-level railway power conditioners have been widely studied due to their modular structure, easy expansion, low-voltage module cascading suitable for high-voltage operation, and the elimination of bulky step-down transformers. At present, modular multi-level railway power conditioners are mainly divided into three-arm multi-level structures and four-arm multi-level structures. Although the four-arm multi-level has a symmetrical structure and simple control, the number of phase units increases and the cost of system operation is high. Therefore, the three-arm multi-level structure has also received widespread attention. However, although the three-arm multi-level structure omits one phase unit, the three phase units operate in an asymmetric three-phase voltage state, which leads to serious differences in the arm current stress between the three phase units. The long-term operation of the system in this state is likely to cause thermal stress differences between the phase units, resulting in differences in reliability between the phase units, threatening the long-term safe and reliable operation of the system. Summary of the invention

[0004] Purpose of the invention: In order to overcome the deficiencies in the prior art, a modular multi-level railway power regulator bridge arm current optimization method is provided, which does not require additional hardware circuits. It can not only compensate for the reactive power of the traction power supply system and suppress the negative sequence component, but also optimize the current stress distribution of the bridge arm, reduce the device phase unit loss and temperature fluctuations, and effectively improve the reliability of the system.

[0005] Technical solution: To achieve the above object, the present invention provides a modular multi-level railway power regulator bridge arm current optimization method, comprising the following steps:

[0006] S1: Calculate the bridge arm current stress data of modular multi-level railway power regulator;

[0007] S2: Based on the bridge arm current stress data, the zero-sequence injection component is set, and the zero-sequence injection component is optimized to obtain the optimal zero-sequence injection component;

[0008] S3: Inject the optimal zero-sequence injection component into the modulation signal, perform current stress optimization control, and output a pulse signal.

[0009] Furthermore, the step S1 includes calculating the instantaneous values ​​of the power of the three bridge arms and calculating the DC component of the bridge arm circulating current in each phase unit in sequence, thereby obtaining the relationship between the bridge arm circulating currents of each phase unit.

[0010] Furthermore, the step S1 specifically includes:

[0011] A1: Calculate the instantaneous value of the power of the three bridge arms;

[0012] According to Kirchhoff's voltage law, the voltage equation of the a-phase bridge arm is expressed as:

[0013]

[0014] Among them, u pa is the voltage of the upper bridge arm of phase a, u na is the lower bridge arm voltage, u ac is the voltage of the α power supply arm, U dc is the DC bus voltage, u co is the voltage between phase c and the midpoint of the DC bus; similarly, the voltage equations of the bridge arms of phase b and phase c are:

[0015] and

[0016] Subtract the above equation from the following equation and add them together to get:

[0017] u ac +u bc +3u co =0(3) According to Kirchhoff's current law, the currents of the upper and lower bridge arms of phase a are:

[0018]

[0019] Among them, i pa 、i na are the upper and lower bridge arm currents of phase a respectively, i za is the a-phase bridge arm circulation, i ac and i bc The grid-side current of the converter is respectively; similarly, the relationship between the bridge arm currents of phase b and phase c is respectively:

[0020] and

[0021] The instantaneous power of each bridge arm is calculated from the voltage and current of each phase unit bridge arm:

[0022] and

[0023] The instantaneous power of the upper and lower bridge arms is superimposed to obtain the power of each phase unit:

[0024]

[0025] A2: Calculate the DC component of the bridge arm circulating current in each phase unit;

[0026] According to the V / v traction power supply system structure, the voltage of the two traction arms can be written as:

[0027]

[0028] The compensation current command values ​​of the converters on both sides are:

[0029]

[0030] Among them, I D is the active component of the compensation current, I Q is the reactive component of the compensation current;

[0031] According to formula (7), the DC component is 0, so the relationship between the circulating currents of each phase unit bridge arm is obtained as follows:

[0032]

[0033] From (10), the DC components of the three-phase bridge arm current of the three-arm modular multi-level railway power conditioner are not equal when there is no zero-sequence component injection, and there are obvious differences in the stress of the bridge arm current.

[0034] Furthermore, step S2 sequentially includes calculating the instantaneous power after the zero-sequence component is injected, calculating the DC component of the bridge arm after the zero-sequence component is injected, and optimizing the amplitude and phase angle of the injected zero-sequence component, thereby obtaining the optimal zero-sequence injection component.

[0035] Furthermore, the step S2 specifically includes:

[0036] B1: Calculate the instantaneous power after injecting the zero-sequence component;

[0037] The injected zero-sequence component is assumed to be:

[0038]

[0039] The voltage of the upper and lower bridge arms is updated as follows:

[0040]

[0041] Similarly, the power between each phase unit of the b-phase and c-phase bridge arms is calculated;

[0042] B2: Calculate the DC component of the bridge arm after the zero-sequence component is injected;

[0043] According to the DC component of the phase unit power being 0, the expression of the DC current circulating in the bridge arm after the zero-sequence component is injected is as follows:

[0044]

[0045] The DC component of the bridge arm current is not only related to the amplitude of the injected zero-sequence component U o It is also related to the phase angle of the injected zero-sequence component. related;

[0046] B3: Optimization of the amplitude and phase angle of the injected zero-sequence component;

[0047] According to the current stress expression, a three-dimensional curve of the bridge arm current is drawn, and the zero-sequence component U corresponding to the optimal bridge arm stress that maximizes the current stress is selected with the bridge arm modulation signal not overshooting as the constraint condition. oopt and As the optimal injection amount.

[0048] Furthermore, the acquisition of the modulated signal in step S3 includes:

[0049] C1: DC voltage outer loop control;

[0050] Sampling DC bus voltage U dc , the DC voltage reference value U dc ref Subtract the sampled value and pass the PI controller, the output of the voltage outer loop is the positive sequence active current reference value i dref + ;

[0051] C2: bridge arm current inner loop control;

[0052] Sample the voltage u of the two traction networks respectively ac 、u bc , and the current i on the grid side of the converter ac 、i bc and -i ac -i bc ; The grid-side voltage is transformed through positive and negative sequence abc / dq to generate positive sequence active and reactive voltage E respectively d + 、E q + and negative sequence active and reactive voltage E d - 、Eq - Similarly, the AC side current of the modular multi-level railway power regulator is transformed through positive and negative sequence abc / dq to obtain positive sequence active current and positive sequence reactive current i d + 、i q + , negative sequence active current, negative sequence reactive current i d - 、i q - In addition, according to the compensation current of the converter and its positive and negative sequence conversion, the inner loop current reference value i is obtained qref + 、i dref - and i qref - The positive and negative sequence voltages and positive and negative sequence currents are decoupled and controlled through their respective current inner loops, and their outputs are respectively transformed through the positive and negative sequence dq / abc inverse transformation, and the AC signals generated by the positive and negative sequences are superimposed to obtain the modulation signal.

[0053] Furthermore, in step S3, the optimal zero-sequence voltage amplitude U oopt and phase angle Injected into the modulation signal to perform capacitor voltage balance control.

[0054] Furthermore, the capacitor voltage balance control method in step S3 is: the modulation signal is passed through the nearest level approximation modulation (NLM), and the voltage of each sub-module and the bridge arm current are sampled, and the capacitor voltage sorting algorithm is used to achieve the balance control of the capacitor voltage, and finally the pulse signals Sai, Sbi and Sci are generated and output to each sub-module to drive each switching device.

[0055] The method of the present invention changes the power distribution between the three-phase units by injecting zero-sequence voltage components into the phase units, thereby adjusting the stress of the bridge arm current of each phase unit; optimizes the amplitude and phase of the injected zero-sequence components respectively to obtain the relationship between the injected zero-sequence components and the bridge arm current stress; and selects the optimal zero-sequence injection component with the minimum current stress of the bridge arm with the worst current as the optimization goal.

[0056] The method of the present invention can improve the power quality of the railway traction network and effectively improve the current distribution between the three phase units, thereby improving the operational reliability of the system.

[0057] In combination with the above contents, the method of the present invention can be summarized as follows:

[0058] 1) Derive the power distribution between phase units and the distribution characteristics of the bridge arm current of each phase unit before and after the zero-sequence component is injected; the power distribution between phase units is affected not only by the amplitude of the injected fundamental frequency component, but also by the initial phase angle of the injection;

[0059] 2) Draw a three-dimensional curve between the DC component of the bridge arm current and the amplitude and phase angle of the injected zero-sequence component, and thereby find a set that can optimize the bridge arm current stress. Combined with the constraint that the system modulation signal does not over-modulate after the zero-sequence component is injected, the above set is further constrained to obtain a constrained set. On this basis, the solution that minimizes the current stress of the bridge arm in the worst working condition is selected as the optimal zero-sequence injection amplitude and phase angle;

[0060] 3) Through the voltage and current dual closed-loop control, capacitor voltage balance control strategy and zero-sequence voltage optimization results, pulse signals of the corresponding devices of each sub-module that meet the above conditions are generated.

[0061] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0062] 1. By analyzing the instantaneous power of the three-arm modular multi-level railway power conditioner, the DC current distribution characteristics between phase units are derived, and the causes of the bridge arm current differences are analyzed. On this basis, the method of the present invention realizes the redistribution of the power of the three-phase phase unit among the three phases by optimizing the amplitude and phase of the zero-sequence voltage, effectively reducing the stress of the bridge arm current and reducing the probability of device failure.

[0063] 2. Since the method of the present invention injects zero-sequence components into each modulation signal, it will not affect the line voltage and current on the AC side; in addition, the voltage and current of the DC port will remain unchanged. Therefore, the method of the present invention not only improves the power quality on the three-phase grid side, but also optimizes the thermal stress between phase units, which is beneficial to the design of the heat dissipation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 It is a schematic diagram of the topology of the traction power supply system and the modular multi-level railway power regulator;

[0065] Figure 2 Schematic diagram for solving the zero-sequence component injection of the phase unit bridge arm current;

[0066] Figure 3 Schematic diagram of bridge arm current optimization control of modular multi-level railway power regulator. DETAILED DESCRIPTION

[0067] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0068] like Figure 1 As shown, the present invention provides a modular multi-level railway power regulator bridge arm current optimization method, comprising the following steps:

[0069] S1: Calculate the bridge arm current stress data of modular multi-level railway power regulator;

[0070] Reference Figure 1 , step S1 specifically includes:

[0071] A1: Calculate the instantaneous value of the power of the three bridge arms;

[0072] According to Kirchhoff's voltage law, the voltage equation of the a-phase bridge arm is expressed as:

[0073]

[0074] Among them, u pa is the voltage of the upper bridge arm of phase a, u na is the lower bridge arm voltage, u ac is the voltage of the α power supply arm, U dc is the DC bus voltage, u co is the voltage between phase c and the midpoint of the DC bus; similarly, the voltage equations of the bridge arms of phase b and phase c are:

[0075]

[0076] Subtract the above equation from the following equation and add them together to get:

[0077] u ac +u bc +3u co =0(3) According to Kirchhoff's current law, the currents of the upper and lower bridge arms of phase a are:

[0078]

[0079] Among them, i pa 、i na are the upper and lower bridge arm currents of phase a respectively, i za is the a-phase bridge arm circulation, i ac and i bc The grid-side current of the converter is respectively; similarly, the relationship between the bridge arm currents of phase b and phase c is respectively:

[0080] and

[0081] The instantaneous power of each bridge arm is calculated from the voltage and current of each phase unit bridge arm:

[0082] and

[0083] The instantaneous power of the upper and lower bridge arms is superimposed to obtain the power of each phase unit:

[0084]

[0085] A2: Calculate the DC component of the bridge arm circulating current in each phase unit;

[0086] According to the V / v traction power supply system structure, the voltage of the two traction arms can be written as:

[0087]

[0088] The compensation current command values ​​of the converters on both sides are:

[0089]

[0090] Among them, I D is the active component of the compensation current, I Q is the reactive component of the compensation current;

[0091] According to formula (7), the DC component is 0, so the relationship between the circulating currents of each phase unit bridge arm is obtained as follows:

[0092]

[0093] From (10), the DC components of the three-phase bridge arm current of the three-arm modular multi-level railway power conditioner are not equal when there is no zero-sequence component injection, and there are obvious differences in the stress of the bridge arm current.

[0094] S2: Based on the bridge arm current stress data, the zero-sequence injection component is set, and the zero-sequence injection component is optimized to obtain the optimal zero-sequence injection component;

[0095] Reference Figure 2 , step S2 specifically includes:

[0096] B1: Calculate the instantaneous power after injecting the zero-sequence component;

[0097] The injected zero-sequence component is assumed to be:

[0098]

[0099] The voltage of the upper and lower bridge arms is updated as follows:

[0100]

[0101] Similarly, the power between each phase unit of the b-phase and c-phase bridge arms is calculated;

[0102] B2: Calculate the DC component of the bridge arm after the zero-sequence component is injected;

[0103] According to the DC component of the phase unit power being 0, the expression of the DC current circulating in the bridge arm after the zero-sequence component is injected is as follows:

[0104]

[0105] The DC component of the bridge arm current is not only related to the amplitude of the injected zero-sequence component U o It is also related to the phase angle of the injected zero-sequence component. related;

[0106] B3: Optimization of the amplitude and phase angle of the injected zero-sequence component;

[0107] According to the current stress expression, a three-dimensional curve of the bridge arm current is drawn, and the zero-sequence component U corresponding to the optimal bridge arm stress that maximizes the current stress is selected with the bridge arm modulation signal not overshooting as the constraint condition. oopt and As the optimal injection amount.

[0108] S3: injecting the optimal zero-sequence injection component into the modulation signal, performing current stress optimization control, and outputting a pulse signal;

[0109] Reference Figure 3 , step S3 specifically includes:

[0110] C1: DC voltage outer loop control;

[0111] Sampling DC bus voltage U dc , the DC voltage reference value U dc ref Subtract the sampled value and pass the PI controller, the output of the voltage outer loop is the positive sequence active current reference value i dref + ;

[0112] C2: bridge arm current inner loop control;

[0113] Sample the voltage u of the two traction networks respectively ac 、u bc , and the current i on the grid side of the converter ac 、i bc and -i ac -i bc ; The grid-side voltage is transformed through positive and negative sequence abc / dq to generate positive sequence active and reactive voltage E respectively d+ 、E q + and negative sequence active and reactive voltage E d - 、E q - Similarly, the AC side current of the modular multi-level railway power regulator is transformed through positive and negative sequence abc / dq to obtain positive sequence active current and positive sequence reactive current i d + 、i q + , negative sequence active current, negative sequence reactive current i d - 、i q - In addition, according to the compensation current of the converter and its positive and negative sequence conversion, the inner loop current reference value i is obtained qref + 、i dref - and i qref - ; The positive and negative sequence voltages and positive and negative sequence currents are decoupled and controlled through their respective current inner loops, and their outputs are respectively transformed through the positive and negative sequence dq / abc inverse transformation, and the AC signals generated by the positive and negative sequences are superimposed to obtain the modulation signal;

[0114] C3: Set the optimal zero-sequence voltage amplitude U oopt and phase angle Inject it into the modulation signal to control the capacitor voltage balance; pass the modulation signal through the nearest level approach modulation (NLM), sample the voltage of each sub-module and the bridge arm current, use the capacitor voltage sorting algorithm to achieve capacitor voltage balance control, and finally generate pulse signals Sai, Sbi and Sci to output to each sub-module to drive each switching device.

Claims

1. A modular multi-level railway power regulator bridge arm current optimization method, characterized in that: The steps include: S1: Calculate the bridge arm current stress data of modular multi-level railway power regulator; S2: Based on the bridge arm current stress data, the zero-sequence injection component is set, and the zero-sequence injection component is optimized to obtain the optimal zero-sequence injection component; S3: Inject the optimal zero-sequence injection component into the modulation signal, perform current stress optimization control, and output a pulse signal.

2. A modular multi-level railway power regulator bridge arm current optimization method according to claim 1, characterized in that: The step S1 includes calculating the instantaneous value of the power of the three bridge arms and calculating the DC component of the bridge arm circulating current in each phase unit in sequence, thereby obtaining the relationship between the bridge arm circulating currents of each phase unit.

3. A modular multi-level railway power regulator bridge arm current optimization method according to claim 1, characterized in that: The step S1 specifically includes: A1: Calculate the instantaneous value of the power of the three bridge arms; According to Kirchhoff's voltage law, the voltage equation of the a-phase bridge arm is expressed as: Among them, u pa is the voltage of the upper bridge arm of phase a, u na is the lower bridge arm voltage, u ac is the voltage of the α power supply arm, U dc is the DC bus voltage, u co is the voltage between phase c and the midpoint of the DC bus; similarly, the voltage equations of the bridge arms of phase b and phase c are: Subtract the above equation from the following equation and add them together to get: and ac +and bc +3u co =0(3) According to Kirchhoff's current law, the currents of the upper and lower bridge arms of phase a are: Among them, i pa 、i na are the upper and lower bridge arm currents of phase a respectively, i za is the a-phase bridge arm circulation, i ac and i bc The grid-side current of the converter is respectively; similarly, the relationship between the bridge arm currents of phase b and phase c is respectively: The instantaneous power of each bridge arm is calculated from the voltage and current of each phase unit bridge arm: The instantaneous power of the upper and lower bridge arms is superimposed to obtain the power of each phase unit: A2: Calculate the DC component of the bridge arm circulating current in each phase unit; According to the V / v traction power supply system structure, the voltage of the two traction arms can be written as: The compensation current command values ​​of the converters on both sides are: Among them, I D is the active component of the compensation current, I Q is the reactive component of the compensation current; According to formula (7), the DC component is 0, so the relationship between the circulating currents of each phase unit bridge arm is obtained as follows:

4. A modular multi-level railway power regulator bridge arm current optimization method according to claim 1, characterized in that: The step S2 includes calculating the instantaneous power after the zero-sequence component is injected, calculating the DC component of the bridge arm after the zero-sequence component is injected, and optimizing the amplitude and phase angle of the injected zero-sequence component, thereby obtaining the optimal zero-sequence injection component.

5. A modular multi-level railway power regulator bridge arm current optimization method according to claim 4, characterized in that: The step S2 specifically includes: B1: Calculate the instantaneous power after injecting the zero-sequence component; The injected zero-sequence component is assumed to be: The voltage of the upper and lower bridge arms is updated as follows: Similarly, the power between each phase unit of the b-phase and c-phase bridge arms is calculated; B2: Calculate the DC component of the bridge arm after the zero-sequence component is injected; According to the DC component of the phase unit power being 0, the expression of the DC current circulating in the bridge arm after the zero-sequence component is injected is as follows: The DC component of the bridge arm current is not only related to the amplitude of the injected zero-sequence component U o It is also related to the phase angle of the injected zero-sequence component. related; B3: Optimization of the amplitude and phase angle of the injected zero-sequence component; According to the current stress expression, a three-dimensional curve of the bridge arm current is drawn, and the zero-sequence component U corresponding to the optimal bridge arm stress that maximizes the current stress is selected with the bridge arm modulation signal not overshooting as the constraint condition. oopt and As the optimal injection quantity.

6. A modular multi-level railway power regulator bridge arm current optimization method according to claim 1, characterized in that: The acquisition of the modulated signal in step S3 includes: C1: DC voltage outer loop control; Sampling DC bus voltage U dc , the DC voltage reference value U dc ref Subtract the sampled value and pass the PI controller, the output of the voltage outer loop is the positive sequence active current reference value i dref + ; C2: bridge arm current inner loop control; Sample the voltage u of the two traction networks respectively ac 、u bc , and the current i on the grid side of the converter ac 、i bc and -i ac -i bc ; The grid-side voltage is transformed through positive and negative sequence abc / dq to generate positive sequence active and reactive voltage E respectively d + 、E q + and negative sequence active and reactive voltage E d - 、E q - Similarly, the AC side current of the modular multi-level railway power regulator is transformed through positive and negative sequence abc / dq to obtain positive sequence active current and positive sequence reactive current i d + 、i q + , negative sequence active current, negative sequence reactive current i d - 、i q - In addition, according to the compensation current of the converter and its positive and negative sequence conversion, the inner loop current reference value i is obtained qref + 、i dref - and i qref - The positive and negative sequence voltages and positive and negative sequence currents are decoupled and controlled through their respective current inner loops, and their outputs are respectively transformed through the positive and negative sequence dq / abc inverse transformation, and the AC signals generated by the positive and negative sequences are superimposed to obtain the modulation signal.

7. A modular multi-level railway power regulator bridge arm current optimization method according to claim 5, characterized in that: In step S3, the optimal zero-sequence voltage amplitude U oopt and phase angle Injected into the modulation signal to perform capacitor voltage balance control.

8. A modular multi-level railway power regulator bridge arm current optimization method according to claim 7, characterized in that: The capacitor voltage balance control method in step S3 is: the modulation signal is modulated by the nearest level approximation, and the voltage of each sub-module and the bridge arm current are sampled, and the capacitor voltage sorting algorithm is used to achieve the capacitor voltage balance control, and finally the pulse signals Sai, Sbi and Sci are generated and output to each sub-module to drive each switch device.

Images