CN102394557A - Hybrid parallel type high-voltage direct current traction power supply current transformer and control method thereof - Google Patents

Abstract

The invention relates to a hybrid parallel type high-voltage direct current traction power supply current transformer and a control method thereof. The hybrid parallel type high-voltage direct current traction power supply current transformer is characterized by comprising a set of pulse width modulation (PWM) rectifier units and a set of diode rectifier units, wherein both an input end of the PWM rectifier units and an input end of the diode rectifier units are connected with an alternating current electric network, and an output end of the PWM rectifier units and an output end of the diode rectifier units are connected in parallel to realize high-voltage direct current output. Because the PWM rectifier units and the diode rectifier units are connected in series, the direct current output voltage of the entire current transformer is improved, the power supply distance is prolonged, and the contact net loss is reduced. Meanwhile, equipment investment is reduced, and the reliability of a system is improved. The hybrid parallel type high-voltage direct current traction power supply current transformer and the control method thereof can be widely applied to urban railway transit traction power supply systems.

Description

A hybrid parallel high-voltage DC traction power supply converter device and its control method

technical field

The invention relates to a high-voltage direct current traction power supply conversion device and a control method thereof, in particular to a hybrid parallel high-voltage direct current traction power supply conversion device and a control method for supplying power to urban rail transit vehicles.

Background technique

At present, the traction power supply conversion device of urban rail transit in my country still uses diode rectifiers, and the power supply voltage is 750V or 1500V. This power supply method has been used for decades. Its biggest advantage is that the device structure is simple and the technology is relatively mature. However, this traditional power supply scheme also has the following problems: 1. Due to the use of diode rectifiers, the energy can only be unidirectional Therefore, the energy generated by vehicle braking cannot be fed back to the grid, and is usually consumed by resistors, resulting in a great waste of energy. 2. The DC output voltage is uncontrollable and has a large fluctuation range, which is not conducive to the safe, reliable and economical operation of the vehicle. 3. The catenary network has a large voltage drop, and the distance between power supply stations is short, usually no more than 3 to 4 kilometers, resulting in a large number of required power supply stations and a large construction investment.

The PWM (Pulse Width Modulation) rectifier has the advantages of bidirectional energy flow, high power factor, and controllable DC output voltage. Applying the PWM rectifier to the urban rail transit traction power supply system can not only realize the feedback of train braking energy, save electric energy, and keep the DC voltage stable; at the same time, if the DC power supply can be increased to more than 1.5kV, the power supply distance can also be extended. Reducing the number of power supply stations and catenary loss has great practical application value, but compared with traditional diode rectifiers, PWM rectifiers are at a disadvantage in terms of price, reliability, maintenance, and overload capacity. In fact, for the urban rail transit traction power supply system, the required traction capacity is usually more than twice the braking capacity, so from the economic point of view, the power supply scheme based on the full PWM rectifier is not cost-effective.

Contents of the invention

In view of the above problems, the object of the present invention is to provide a DC traction power supply voltage that can increase the power supply distance, reduce the number of power supply stations, reduce catenary loss, and improve system reliability while realizing the feedback and reuse of train braking energy. Hybrid parallel high-voltage DC traction power supply converter device and its control method.

In order to achieve the above object, the present invention adopts the following technical solutions: a hybrid parallel high-voltage DC traction power supply converter, characterized in that it includes a set of PWM rectifier units and a set of diode rectifier units, the input of the PWM rectifier units The output terminal of the PWM rectifier unit and the output terminal of the diode rectifier unit are connected in parallel to realize high-voltage direct current output.

The PWM rectifier unit includes a multi-winding transformer, several PWM rectifier units and several control units, the multi-winding transformer is composed of a primary winding and a plurality of secondary windings, the number of the PWM rectifier units is the same as the number of the PWM rectifier units The number of secondary windings of the multi-winding transformer is set correspondingly; the primary winding of the multi-winding transformer is connected to the AC power grid, and each secondary winding is connected to one of the PWM rectifier units, and the DC output terminals of each of the PWM rectifier units are sequentially connected in series, and each of the PWM rectifier units is connected to one of the control units, and the control unit controls the operation of the PWM rectifier units.

Each of the control units is composed of four data acquisition units, a current loop control unit, a phase-locked unit, a voltage loop control unit and a pulse generation unit; The two-phase alternating current of the PWM rectifier unit is transmitted to the current loop control unit, and the second data acquisition unit transmits the collected primary winding voltage of the multi-winding transformer to the current through the phase-locked unit. ring control unit, the third and fourth data acquisition units respectively transmit the collected DC voltage and DC current of the PWM rectifier unit to the voltage loop control unit; Subtract the product of the DC current and the droop slope from the given value of the load voltage and perform PI calculation, and the obtained current value is input into the current loop control unit; the voltage and current signals transmitted to the current loop control unit are carried out After the coordinate transformation and PI calculation processing, the pulse generating unit converts it into a driving pulsation signal, and then returns to the PWM rectifier unit to realize its control.

The PWM rectifier unit includes a power device and a DC support capacitor, and the PWM rectifier unit adopts a two-level or three-level three-phase voltage type PWM rectifier main circuit.

The power device is an IGBT power module, and the DC support capacitor is a metal film capacitor.

The diode rectifier unit includes a phase-shifting transformer and several diode rectifier units, the phase-shifting transformer is composed of a primary winding and a plurality of secondary windings, the number of the diode rectifier units is the same as that of the phase-shifting transformer The number of secondary windings is set correspondingly; the primary winding of the phase-shifting transformer is connected to the AC power grid, each secondary winding is connected to one of the diode rectifier units, and the DC output terminals of each diode rectifier unit are connected in series.

Each secondary winding of the phase-shifting transformer is connected in a delta extension mode.

(2)第二个数据采集单元采集多绕组变压器原边绕组电压互感器输出的两相交流电网电压u_a和u_b，并由锁相单元进行锁相，得到电网电压同步角θ；(3)第一个数据采集单元将采集到的PWM整流器单元的两相交流电流i_a和i_b输入电流环控制单元内，将其转换到同步旋转坐标系下得到i_d和i_q；(4)将同步旋转坐标系下得到的d、q轴电流i_d和i_q分别与电流给定值

和

相减，并对其差值分别进行PI运算，得到同步旋转坐标系下脉宽调制电压U_d、U_q；(5)将同步旋转坐标系电压U_d、U_q转换到静止坐标系后输入脉冲产生单元，并采用三电平空间矢量脉宽调制算法产生各IGBT开关管的PWM脉冲信号，实现对PWM整流器单元的控制。The control method for realizing the above-mentioned hybrid parallel high-voltage DC traction power supply converter device includes the following steps: (1) firstly, the voltage loop control is performed in the voltage loop control unit, and the fourth and third data acquisition units respectively collect The DC current I _dc and the DC voltage U _dc of the PWM rectifier unit are both input to the voltage loop control unit, and the DC current I _dc is multiplied by the preset droop slope K _dp and then subtracted from the given value of the DC no-load voltage U _k After that, subtract it from the DC voltage U _dc and perform PI operation to obtain the d-axis active current given value of the current loop control unit

(2) The second data acquisition unit collects the two-phase AC grid voltage u _a and u _b output by the primary winding voltage transformer of the multi-winding transformer, and the phase locking unit performs phase locking to obtain the grid voltage synchronization angle θ; (3 ) The first data acquisition unit inputs the collected two-phase AC currents i _a and i _b of the PWM rectifier unit into the current loop control unit, and converts them to the synchronous rotating coordinate system to obtain i _d and i _q ; (4) The d, q axis currents i _d and i _q obtained under the synchronous rotating coordinate system are respectively compared with the current given value

and

Subtract, and perform PI operation on the difference respectively to obtain the pulse width modulation voltage U _d , U _q in the synchronous rotating coordinate system; (5) Convert the synchronous rotating coordinate system voltage U _d , U _q to the stationary coordinate system and input The pulse generation unit adopts the three-level space vector pulse width modulation algorithm to generate the PWM pulse signal of each IGBT switch tube to realize the control of the PWM rectifier unit.

Each of the PWM rectifier units adopts an external characteristic droop control method based on load current feedforward.

The present invention has the following advantages due to the adoption of the above technical scheme: 1. The present invention improves the DC output voltage of the whole converter due to the adoption of the PWM rectifier unit and the diode rectifier unit in series, prolongs the power supply distance, and reduces the catenary loss. 2. The present invention is based on the hybrid structure of the PWM rectifier unit and the diode rectifier unit, fully utilizes the advantages of the two, while realizing the feedback and reuse of the train braking energy, reduces the equipment investment as much as possible, and improves the reliability of the system . 3. In the present invention, since each secondary winding of the phase-shifting transformer in the diode rectifier unit adopts the extension triangle connection mode, the output voltage phase difference of each secondary winding is 60/n electrical angle, thereby forming multi-pulse rectification, reducing The DC output voltage ripple and AC current harmonics of the entire diode rectifier unit are eliminated. 4. The present invention ensures DC series voltage equalization of each PWM unit and load distribution between the PWM rectifier unit and the diode rectifier unit by controlling the DC output characteristics of each PWM rectifier unit. The invention can be widely used in urban rail transit traction power supply systems.

Description of drawings

Fig. 1 is the overall structure schematic diagram of the present invention;

Fig. 2 is a schematic diagram of the control principle of the PWM rectifier unit of the present invention;

Fig. 3 is a schematic diagram of the structure of the diode rectifier unit in the 9kY hybrid parallel high-voltage DC traction power supply conversion device of the present invention;

Fig. 4 is a schematic structural diagram of the PWM rectifier unit in the 9kY hybrid parallel high-voltage DC traction power supply converter device of the present invention;

Fig. 5 is the main circuit topology of the three-level PWM rectifier unit of the present invention;

Fig. 6 is a schematic diagram of the droop characteristic curve of the hybrid parallel high-voltage DC traction power supply conversion control method of the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, the hybrid parallel connection type high-voltage DC traction power supply conversion device of the present invention includes a set of PWM (pulse width modulation) rectifier unit 10 and a set of diode rectifier unit 20, the input end of PWM rectifier unit 10 and the diode rectifier unit The input ends of 20 are all connected to the AC power grid in the prior art, and after the output end of the PWM rectifier unit 10 and the output end of the diode rectifier unit 20 are connected in parallel, they are used as the output end of the hybrid parallel high-voltage DC traction power supply conversion device of the present invention to realize High voltage DC output.

Wherein, the PWM rectifier unit 10 includes a multi-winding transformer 11, several PWM rectifier units 12 and several control units 13, the multi-winding transformer 11 is composed of a primary winding and a plurality of secondary windings, the number of PWM rectifier units 12 The number of windings on the secondary side of the multi-winding transformer 11 is set correspondingly. The primary winding of the multi-winding transformer 11 is connected to the AC grid, and each secondary winding is connected to a PWM rectifier unit 12, and the DC output terminals of each PWM rectifier unit 12 are connected in series to realize high-voltage DC output. And each PWM rectifier unit 12 is connected to a control unit 13 , and the control unit 13 controls the operation of the PWM rectifier unit 12 .

Diode rectifier unit 20 comprises a phase-shifting transformer 21 and several diode rectifier units 22, phase-shifting transformer 21 is made up of a primary side winding and a plurality of secondary side windings, the number of diode rectifier unit 22 and the secondary side of phase-shifting transformer 21 The number of windings is set accordingly. The primary winding of the phase-shifting transformer 21 is connected to the AC power grid, and each secondary winding is connected to a diode rectifier unit 22, and the DC output terminals of each diode rectifier unit 22 are also connected in series to realize high-voltage output.

In the above embodiments, the secondary windings of the multi-winding transformer 11 in the PWM rectifier unit 10 are connected in the same way, and the short-circuit impedance of each secondary winding is used to replace the AC side inductance of the PWM rectifier unit 12, thereby simplifying the system structure.

In the above-mentioned embodiments, the PWM rectifier unit 12 includes a power device and a DC support capacitor, which can adopt a two-level or three-level three-phase voltage type PWM rectifier main circuit, the power device adopts an IGBT power module, and the DC support capacitor adopts a metal film capacitance.

In the above embodiments, each control unit 13 is composed of four data acquisition units 14 , one current loop control unit 15 , one phase lock unit 16 , one voltage loop control unit 17 and one pulse generation unit 18 . Among them, the first data acquisition unit 14 transmits the collected two-phase AC current of the PWM rectifier unit 12 to the current loop control unit 15; the second data acquisition unit 14 transmits the collected primary winding voltage of the multi-winding transformer 11 It is transmitted to the current loop control unit 15 through the phase-lock unit 16; the third and fourth data acquisition units 14 transmit the DC voltage _Udc and _{the DC} current Idc of the PWM rectifier unit 12 collected to the voltage loop control unit respectively Within 17. The voltage loop control unit 17 subtracts the DC voltage U _dc from the received DC voltage U _dc after subtracting the product of the DC current I _dc and the droop slope K _dp from the given value U k of the DC no-load voltage, and performs a PI operation (proportional integral operation), The obtained current value is input into the current loop control unit 15 . The various voltages and current signals transmitted to the current loop control unit 15 are subjected to coordinate transformation and PI calculation processing, and are converted into driving pulsation signals by the pulse generation unit 18, and then returned to the PWM rectifier unit 12 to realize the control of the PWM rectifier unit 12. control.

In the above-mentioned embodiments, the secondary windings of the phase-shifting transformer 21 in the diode rectifier unit 20 are all connected in a delta extension mode, so that the phase difference of the output voltages of the secondary windings is 60/n electrical degrees, thereby forming a multi-pulse rectification , reducing the DC output voltage ripple and AC current harmonics of the hybrid parallel high-voltage DC traction power supply converter device of the present invention.

As shown in Figure 2, each PWM rectifier unit 12 in the hybrid parallel high-voltage DC traction power supply converter device of the present invention adopts an external characteristic droop control method based on load current feedforward to ensure that each PWM rectifier unit 12 is connected in series to equalize voltage, and Load sharing between the PWM rectifier unit 10 and the diode rectifier unit 20 . Then the hybrid parallel high-voltage DC traction power supply conversion control method of the present invention includes the following steps:

直流电压闭环给定值与直流电压U_dc相减，差值进行PI运算，最后得到电流环控制单元15的d轴有功电流给定值

1) First, the voltage loop control is carried out in the voltage loop control unit 17, and the DC current _Idc and the DC voltage _Udc of the PWM rectifier unit 12 collected respectively are input to the voltage loop by the fourth and the third data acquisition unit 14. In the control unit 17, the DC current I _dc is multiplied by the preset droop slope K _dp and then subtracted from the given value U _k of the DC no-load voltage, and the difference is used as the given value of the closed-loop DC voltage

DC voltage closed-loop given value Subtract it from the DC voltage _Udc , and perform PI calculation on the difference, and finally obtain the given value of the d-axis active current of the current loop control unit 15

2) Phase-lock operation, the second data acquisition unit 14 collects the two-phase AC grid voltages u _a and u _b output by the primary winding voltage transformer of the multi-winding transformer 11, and the phase-locking unit 16 performs phase-locking to obtain the power grid Voltage synchronization angle θ;

3) Coordinate transformation, the two-phase AC current i _a and i _b of the PWM rectifier unit 12 collected by the first data acquisition unit 14 are input into the current loop control unit 15, and converted to the synchronous rotating coordinate system to obtain i _d and _iq ;

和

相减(为了保证功率因数为1，通常都令i_q的电流给定值

)，并对其差值分别进行PI运算，得到同步旋转坐标系下脉宽调制电压U_d、U_q；4) The d, q axis currents i _d and i _q obtained under the synchronous rotating coordinate system are respectively compared with the current given value

and

Subtraction (in order to ensure that the power factor is 1, usually the current given value of i _q

), and perform PI calculations on the difference respectively to obtain the pulse width modulation voltages U _d and U _q in the synchronous rotating coordinate system;

5) After converting the voltages _Ud and _Uq of the synchronous rotating coordinate system to the stationary coordinate system, they are input to the pulse generating unit 18, and a three-level SVPWM (Space Vector Pulse Width Modulation) modulation algorithm is used to generate PWM pulse signals of each IGBT switch tube, The control of the PWM rectifier unit 12 is realized.

In the above embodiments, the voltage loop control unit 17 adopts a PI regulator without static error based on the external characteristic droop control based on the load current feedforward, but the given value of the voltage loop decreases with the increase of the output current.

The present invention will be further introduced through an embodiment below.

Embodiment: As shown in Figure 3, the rated capacity of the diode rectifier unit 20 is 6MW, wherein: the phase-shifting transformer 21 adopts epoxy resin casting dry-type transformer, the capacity is 6MVA, has a primary winding, three secondary windings, The transformation ratio is 35kV/2.4kV/2.4kV/2.4kV, the primary winding is connected by △, and the secondary winding is connected by delta extension, so that the output voltage phase of each secondary winding is +20°, 0°, -20°, Thus, the entire diode rectifier unit 20 constitutes 18-pulse rectification. The capacity of each diode rectifier unit 22 is 2MW, and the rated DC output voltage is 3kV, wherein the diodes are all disc-shaped 6kV high-voltage diodes. The AC side of each diode rectifier unit 22 is respectively connected to a secondary winding of the phase-shifting transformer 21 , and the DC side is connected in series sequentially.

As shown in Figure 4, the capacity of the PWM rectifier unit 10 is also 6MW, wherein: the multi-winding transformer 11 is also a dry-type epoxy resin casting transformer, which has one primary winding, three secondary windings, and the connection of the multi-winding transformer 11 The mode is Yd11, d11, and the transformation ratio of d11 is 35kV/1.8kV/1.8kV/1.8kV, the capacity is 6MVA, and the equivalent short-circuit impedance of the secondary winding is 30%. The capacities of the PWM rectifier units 12 are all 3MW, and the rated DC output voltage is 3kV. The AC side of each PWM rectifier unit 12 is respectively connected to a secondary winding of the multi-winding transformer 11 , and the DC side is connected in series in sequence.

In order to reduce the withstand voltage of power devices and increase the system capacity, each PWM rectifier unit 12 adopts a neutral-point clamped three-level main circuit topology (as shown in FIG. 5 ). Among them, the power device adopts 3300V voltage level IGBT, the switching frequency is 1kHz, and the DC support capacitor adopts metal film capacitor, which has small parasitic inductance, strong ripple current passing ability, and long service life, which is conducive to reducing equipment maintenance costs.

The control method of each PWM rectifier unit 12 adopts external characteristic droop control based on load current feedforward to ensure that each PWM rectifier unit 12 is connected in series for voltage equalization and load distribution between the PWM rectifier unit 10 and the diode rectifier unit 20 .

As shown in FIG. 6 , it is a typical droop characteristic curve of the PWM rectifier unit 12 , kdp is the droop slope, and k _dp =0.15 is taken in this embodiment. In this external droop control method based on load current feedforward, the DC voltage loop still uses a PI regulator without static error, but the given value of the voltage loop decreases with the increase of the output current, and the output of the voltage loop is used as The given value of d-axis active current and the given value of q-axis reactive current are set to zero, and then the active and reactive currents are respectively closed-loop controlled, and the closed-loop control output value is used for SVPWM modulation to finally generate drive pulses.

The above-mentioned embodiments are only used to illustrate the present invention, and the structure and connection mode of each component can be changed. On the basis of the technical solution of the present invention, all improvements to the connection and structure of individual components according to the principles of the present invention and equivalent transformations shall not be excluded from the protection scope of the present invention.

Claims (9)

1. one kind is mixed parallel connection type HVDC traction power supply convertor assembly; It is characterized in that: it comprises a cover PWM Rectification Power Factor and a cover diode rectification unit; The input of the input of said PWM Rectification Power Factor and diode rectification unit all is connected AC network; After the output parallel connection of the output of said PWM Rectification Power Factor and diode rectification unit, realize HVDC output.

2. a kind of mixing parallel connection type HVDC traction power supply convertor assembly as claimed in claim 1; It is characterized in that: said PWM Rectification Power Factor comprises a multi winding transformer, several PWM rectifier units and several control units; Said multi winding transformer is made up of a former limit winding and a plurality of secondary winding, and the number of said PWM rectifier unit is corresponding setting with the said multi winding transformer secondary number of windings; The former limit of said multi winding transformer winding connects said AC network; Each secondary winding connects a said PWM rectifier unit; Each said PWM rectifier unit dc output end is in sequential series; And each said PWM rectifier unit all connects a said control unit, and said control unit is controlled the work of said PWM rectifier unit.

3. a kind of mixing parallel connection type HVDC traction power supply convertor assembly as claimed in claim 2 is characterized in that: each said control unit constitutes by four data collecting units, a current loop control unit, a phase locking unit, a Voltage loop control unit and a pulse generation unit; The said PWM rectifier unit two-phase alternating current that first said data acquisition unit will collect transfers to said current loop control unit; The former limit winding voltage of the said multi winding transformer that second said data acquisition unit will collect transfers to said current loop control unit through said phase locking unit, and the direct voltage and the direct current of the said PWM rectifier unit that the 3rd, the 4th said data acquisition unit will collect respectively transfer to said Voltage loop control unit; Said Voltage loop control unit deducts the direct-flow no load voltage set-point behind the product of direct current and sagging slope and carries out the PI computing, and the current value that obtains is imported in the said current loop control unit; Transfer to after each road voltage, current signal in the said current loop control unit carry out coordinate transform and PI calculation process, through said pulse generation unit convert to drive fluctuating signal after, be back to said PWM rectifier unit and realize its control.

4. like claim 2 or 3 described a kind of mixing parallel connection type HVDC traction power supply convertor assemblys; It is characterized in that: said PWM rectifier unit comprises that power device and direct current support electric capacity, and said PWM rectifier unit adopts two level or three level Three-phase PWM Voltage Rectifier main circuits.

5. a kind of mixing parallel connection type HVDC traction power supply convertor assembly as claimed in claim 4 is characterized in that: said power device adopts the IGBT power model, and said direct current supports electric capacity and adopts metallic film electric capacity.

6. like any described a kind of mixing parallel connection type HVDC traction power supply convertor assembly of claim 1～5; It is characterized in that: said diode rectification unit comprises a phase shifting transformer and several diode rectifier unit; Said phase shifting transformer is made up of a former limit winding and a plurality of secondary winding, and the number of said diode rectifier unit is corresponding setting with the secondary number of windings of said phase shifting transformer; The former limit of said phase shifting transformer winding connects said AC network, and each secondary winding connects a said diode rectifier unit, and each said diode rectifier unit dc output end is in sequential series.

7. a kind of mixing parallel connection type HVDC traction power supply convertor assembly as claimed in claim 6, it is characterized in that: each secondary winding of said phase shifting transformer all adopts the extend-triangle connected mode.

8. realize the control method like any said mixing parallel connection type HVDC traction power supply convertor assembly of claim 1～7, it comprises the steps:

(1) at first carries out Voltage loop control, by the 4th and the 3rd data collecting unit direct current I with the PWM rectifier unit that collects respectively at the Voltage loop control unit _DcWith direct voltage U _DcAll input to the Voltage loop control unit, direct current I _DcWith predefined sagging slope K _DpBack and direct-flow no load voltage set-point U multiply each other _kAfter subtracting each other, with direct voltage U _DcSubtract each other and carry out the PI computing, obtain the d axle active current set-point of current loop control unit

(2) second data collecting units are gathered the two-phase alternating current net voltage u of the former limit of multi winding transformer winding voltage instrument transformer output _aAnd u _b, and advance horizontal lock by phase locking unit, obtain line voltage synchro angle θ;

(3) first data acquisition unit is with the two-phase alternating current i of the PWM rectifier unit that collects _aAnd i _bIn the input current ring control unit, it is transformed under the synchronous rotating frame obtains i _dAnd i _q

(4) with the d that obtains under the synchronous rotating frame, q shaft current i _dAnd i _qRespectively with the electric current set-point

With

Subtract each other, and its difference is carried out the PI computing respectively, obtain pwm voltage U under the synchronous rotating frame _d, U _q

(5) with the synchronous rotating frame voltage U _d, U _qBe transformed into input pulse generation unit after the rest frame, and adopt the 3 level space vector pulse width modulation algorithm to produce the pwm pulse signal of each IGBT switching tube, realize control the PWM rectifier unit.

9. a kind of mixing parallel connection type HVDC traction power supply unsteady flow control method as claimed in claim 8, it is characterized in that: each said PWM rectifier unit all adopts based on the sagging control method of the external characteristic of load-current feedforward.

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