CN104993686B - A kind of single-phase rectifier based on Modular multilevel converter starts method - Google Patents

Abstract

Start method the invention discloses a kind of single-phase rectifier based on Modular multilevel converter, belong to electric and electronic technical field.In the prior art, also, the invention provides a kind of startup method of single-phase rectifier of DC side with bulky capacitor, two processes are specifically included without reference to the startup method of single-phase rectifier of the DC side with bulky capacitor：Uncontrollable rectifier process and energy hole process.The method has filled up the blank of the startup method of single-phase rectifier of the DC side with bulky capacitor, and realizes MMC system smooth steadies and quickly start.

Description

A kind of single-phase rectifier based on Modular multilevel converter starts method

Technical field

The invention belongs to electric and electronic technical field, more particularly, to a kind of based on Modular multilevel converter Single-phase rectifier starts method.

Background technology

Modular multilevel converter (Module Multilevel Converter) is with a wide range of applications, The multiples such as motor driving, static reactive, electric traction, distributed power generation are expanded to by initial flexible direct-current transmission field Field.This causes that the research of MMC is not limited solely to three-phase and field of power transmission, and single-phase MMC is applied to motor and drives, electrically leads Draw, single-phase MMC inverter and rectifier have all turned into another new research fields of MMC.And due to containing substantial amounts of electricity in MMC Hold, before MMC normal works, submodule is no voltage, so need to carry out sub- module capacitance being pre-charged, make its electricity Hold voltage to rise near rated value, the start-up course of the process of the precharge, referred to as MMC.

Startup for MMC, generally there is self-excitation type and separately excited type two ways.Separately excited type mainly passes through external accessory power supply With switch, modules are carried out and is charged；Self-excitation type does not need extra accessory power supply then, by AC network and control plan Slightly, the pre-charge process for MMC submodule electric capacity is completed.

Separately excited type starts scheme due to needing extra accessory power supply, there is that start-up course is cumbersome, the time is long, efficiency is low Shortcoming.

It is many in current MMC systems that scheme is started using self-excitation type, however it is not deep enough for the research of self-excitation type startup scheme Enter, mostly just for the occasion that flexible DC power transmission is applied in MMC, for individually doing single-phase rectifier and DC side as MMC During occasion with bulky capacitor (mF), the start-up course of MMC systems is not only that sub- module capacitance is charged, and should also be included straight Flow the charging of lateral capacitance.For the start-up course of this kind of system, document is not studied it at present.

The content of the invention

For problems of the prior art, the application provides a kind of startup side of single-phase MMC rectifier system Method, wherein by the research of uncontrollable rectifier process and energy hole process and being related to, compared with existing product, realizes MMC systems System smooth steady quickly starts.

To achieve the above object, according to one aspect of the present invention, there is provided one kind is based on Modular multilevel converter Single-phase rectifier start method, the single-phase rectifier include facies unit, DC side, the facies unit is by upper and lower bridge arm structure Into the upper and lower bridge arm is made up of N number of submodule and a bridge arm inductance respectively, and the submodule is carried reversely simultaneously by two The H half-bridge that the switching tube of di- pole pipe is constituted is connected in parallel with a capacitor the midpoint between composition, the upper and lower bridge arm inductance to hand over again Stream output end, is connected with AC power, and the DC side accesses bulky capacitor, and and direct current network to upper and lower bridge arm loop respectively Connection, it is characterised in that the method is comprised the following steps；

(1) uncontrollable rectifier process

The AC power is by electric capacity that the anti-paralleled diode of the switching tube in the submodule is the submodule And the DC bus capacitor charges, at the end of the process, and the submodule voltage sum V of upper bridge arm is caused_apAnd lower bridge Arm submodule voltage sum V_anAll reach the twice of alternating voltage peak E, DC capacitor voltage sum U_dcAlso AC is reached The twice of voltage peak E；

(2) energy hole process

After the uncontrollable rectifier stage terminates, controlled by the ratio resonance to alternating current, i.e. PR controls make AC defeated Enter fixed power, energy is provided for electric capacity charges；

In the single-phase rectifier normally operation, circulation i can be produced_diffAnd circulation additional reference signal v_diff, use Circulation additional reference signal v_diffControl upper and lower bridge arm energy and value, using circulation i_diffIn fundametal compoment exchanged with described The DC quantity that output end output voltage product is produced controls the difference of upper and lower bridge arm energy；

Electric capacity is continued as by the PR controls to the energy and value, the control of the energy differences and alternating current to fill Electricity so that the capacitance voltage of submodule and the capacitance voltage of DC side reach rated value, then system completion start-up course, enters Steady-working state.

Preferably, the step (1) specifically includes following steps：

1) first process of uncontrollable rectifier, in the uncontrollable rectifier stage with soft start resistance, is limited by soft start resistance The charging current of uncontrollable rectifier stage early stage processed；

2) second process of uncontrollable rectifier, cuts off the uncontrollable rectifier stage of soft start resistance, finally causes upper bridge arm Submodule voltage sum v_apAnd lower bridge arm submodule voltage sum v_anIt is equal to the twice of alternating voltage peak E, DC side electricity Hold voltage sum U_dcAlso it is the twice of AC voltage peak E；

Preferably, the step (2) specifically includes following steps：

1) the energy hole stage one, under the PR control actions of energy hole and alternating current, AC is same with DC side When give submodule transimission power, now the DC component of circulation is to flow to submodule by DC side so that submodule voltage is rapid Rise so that submodule capacitor voltage first reaches rated value；

2) the energy hole stage two, AC in power transmission to submodule, due to the effect of energy hole, submodule By this carrier of the DC component of circulation, DC side is transmitted power to so that DC capacitor voltage rises to rated value, Now the direction of DC component is to flow to DC bus capacitor from submodule in circulation.

In general, to possess following technology compared with prior art, mainly according to above-mentioned technology design of the invention excellent Point：

1st, there is provided a kind of startup method of single-phase MMC rectifier system of DC side with bulky capacitor；

2nd, MMC system smooth steadies are realized quickly to start.

Brief description of the drawings

Fig. 1 is MMC rectifier main circuit structure schematic diagram of the invention；

Fig. 2 is MMC rectifier hardware system schematic diagram of the invention；

Fig. 3 is the flow chart of the startup method of MMC systems of the invention；

Fig. 4 be the uncontrollable rectifier stage of the invention submodule in current flow diagrams；

Fig. 5 (a) is the energy and circulation when first process submodule voltage of energy hole stage of the invention rises The flow graph of DC component；

Fig. 5 (b) is the energy and circulation when second course direct side voltage of energy hole stage of the invention rises The flow graph of DC component；

Fig. 6 is the closed-loop control block diagram of start-up course of the invention.

Specific embodiment

In order to make the purpose , technical scheme and advantage of the present invention be clearer, it is right below in conjunction with drawings and Examples The present invention is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, and It is not used in the restriction present invention.As long as additionally, technical characteristic involved in invention described below each implementation method Not constituting conflict each other can just be mutually combined.

Fig. 1 show the structure chart of MMC systems of the invention.Mainly include AC power AC, AC relay S1, excision Soft electric resistance switch S2, soft upper resistance R1, the submodule SM1-SM16 of MMC, bridge arm reactor Larm, DC bus capacitor C1, C2, D.C. contactor S3, direct current lateral load R2.

Fig. 2 is the overall structure of hardware system, and whole system can be divided into 4 parts, mainly man-machine interface layer, in real time Control and signal transacting layer, transducer side.It is briefly described below for the thing that every aspect is included.

Man-machine interface layer：Mainly include a computer and upper computer software.

Real-time control layer：Mainly DSP and two main control chips of FPGA and its peripheral circuit.

Signal transacting layer：Mainly include optical fiber change-over panel, the detection plate of common signal, the control panel of relay and drive Plate.

Transducer side：Main is exactly the main circuit of converter.

Startup scheme of the invention, wherein AC voltage effective value 220V will be illustrated with an embodiment below；Alternating current Voltage-frequency rate 50Hz；DC side rated voltage 800V；Submodule quantity 16；Submodule rated voltage 100V.

Fig. 3 is the startup protocol procedures figure of the present embodiment.It can be seen that the startup scheme of this example can substantially be divided into 4 Process, respectively：In the uncontrollable rectifier stage with soft start resistance, cut off the uncontrollable rectifier stage of soft start resistance, energy control Process processed one (submodule capacitor voltage uphill process), energy hole process two (DC capacitor voltage uphill process).

Fig. 4 is the flow graph of electric current in the main circuit in the uncontrollable rectifier stage of the present embodiment, it can be seen that AC power is led to It is that submodule electric capacity and DC bus capacitor charge to cross and do not control diode, the submodule voltage sum of upper bridge arm at the end of the process v_apWith lower bridge arm submodule voltage sum v_anIt is equal to 622V, DC capacitor voltage sum U_dcAlso it is 622V.

The flow direction of energy and circulation DC component when Fig. 5 is energy hole stage DC voltage rising of the invention Figure.

Specifically, energy hole principle can be expressed as follows.

Each bridge arm total energy change of variable expression formula be：

In formula, W_ap ^∑、W_an ^∑、v_apref、v_anref、i_ap、i_an、U_dc、e_j ^ref、i_j、i_diff、v_diffRespectively go up the total energy of bridge arm Amount, the bridge arm output reference voltage of the bridge arm output reference voltage of the gross energy of lower bridge arm, upper bridge arm, lower bridge arm, upper bridge arm electricity Stream, lower bridge arm current, DC voltage, equivalent AC output reference voltage, alternating current, bridge arm circulation, circulation additional reference letter Number.

Can be obtained by (1) and (2) two formulas, store gross energy in bridge arm electric capacity, and upper and lower bridge arm energy it Poor change can be expressed as：

The total energy adjustment of bridge arm is can be seen that with control component v by (3) above and (4) two formulas_diffIt is relevant, work as energy When amount sum is less than reference value, it is only necessary to increase v_diff, when energy sum is more than reference value, then need to reduce v_diff。 The control of the difference of upper and lower bridge arm energy, then can be by controlling i_diffIn fundametal compoment so that it multiplies with ac output voltage Product produces a DC quantity to go to control the difference of energy.V in Fig. 5₁It is pressure drop that ac-side current is produced in bridge arm impedance, v_diffIt is pressure drop that circulation is produced in bridge arm impedance, is also the circulation additional reference signal that energy hole effect is produced, v_ap、 v_an、e_v、U_dc/ 2 are respectively upper bridge arm equivalent output voltage, lower bridge arm equivalent output voltage, AC supply voltage and direct current Lateral capacitance voltage.The energy hole stage can also be divided into two processes, as can be seen from Figure, first process, in energy control In the presence of system, AC gives submodule transimission power simultaneously with DC side, and now the DC component of circulation is by direct current effluent To submodule so that submodule voltage rises rapidly.Second process, AC in power transmission to submodule, due to energy The effect of control is measured, submodule transmits power to DC side by this carrier of the DC component of circulation so that DC side electricity Hold voltage and rise to rated value, now the direction of DC component is to flow to DC bus capacitor by submodule in circulation.

Fig. 6 is the closed-loop control block diagram of start-up course of the invention.Part shown in dotted line frame is closed loop energy hole Part, as illustrated, by real-time detection submodule capacitor voltage value, the gross energy and upper and lower bridge arm of bridge arm are tried to achieve respectively Energy differences, respectively as the input of energy sum and the difference controller of energy.Total energy hole is using a PI control Device processed produces an additional DC component to be superimposed upon v_diff, the energy for controlling bridge arm total with this.Similarly, for upper and lower bridge The control of the difference of arm energy, is also, by PI controllers and a series of computing, finally to produce a DC component to be superimposed upon v_diffTo realize the control to energy differences.Alternating current closed loop control is also added into except energy hole part, in start-up course System, it should be noted that for the e that exchange closed-loop control is generated_jSignal can otherwise cause dynamic, it is necessary to add amplitude limit to control Process dash current is very big, or even system can be caused unstable.And digital filter link is then must be added to for energy hole, it is no Then can be because of the strong effect of energy hole, the fluctuation for causing dynamic process Neutron module capacitance voltage violent, so that directly The voltage of stream side and whole bridge arm cannot fast and stable.For producing the U in modulated signal_dc/ 2, it is necessary to use real-time sampling And the signal for coming, and can not be directly to surely final stable state reference value, otherwise system cannot be stablized in dynamic process, and sampling The signal returned is primarily due in start-up course, it is necessary to add digital filter link, and DC capacitor voltage is on continuing Rise and be continually changing, if being not added with digital filter link, the modulated signal of final generation can be influenceed so that the energy of bridge arm is dynamic It is uncontrollable during state.Transmit fixed power by exchanging lateral DC side in start-up course, be submodule electric capacity with it is straight Stream lateral capacitance provides energy, its voltage is risen to rated value, completes start-up course.

As it will be easily appreciated by one skilled in the art that the foregoing is only presently preferred embodiments of the present invention, it is not used to The limitation present invention, all any modification, equivalent and improvement made within the spirit and principles in the present invention etc., all should include Within protection scope of the present invention.

Claims (5)

1. a kind of single-phase rectifier based on Modular multilevel converter (MMC) starts method, and the single-phase rectifier includes Facies unit, DC side, the facies unit are made up of upper and lower bridge arm, and the upper and lower bridge arm is respectively by N number of submodule and a bridge Arm inductance is constituted, and the submodule is in parallel one again by the H half-bridge that two switching tubes with anti-parallel diodes are constituted Electric capacity is constituted, and the midpoint between the upper and lower bridge arm inductance is ac output end, is connected with AC power, the DC side difference Bulky capacitor is accessed to upper and lower bridge arm loop, and is connected with direct current network, it is characterised in that the method is comprised the following steps；

(1) uncontrollable rectifier process

The AC power by electric capacity that the anti-paralleled diode of the switching tube in the submodule is the submodule and The DC bus capacitor charges, and at the end of the process, and causes the submodule voltage sum V of upper bridge arm_apAnd lower bridge arm Submodule voltage sum V_anAll reach the twice of alternating voltage peak E, DC capacitor voltage sum U_dcAlso AC electricity is reached Press the twice of peak E；

(2) energy hole process

After the uncontrollable rectifier stage terminates, controlled by the ratio resonance to alternating current, i.e. PR controls are input into AC solid Fixed power, energy is provided for electric capacity charges；

In the single-phase rectifier normally operation, circulation i can be produced_diffAnd generate circulation additional reference signal v_diff, using ring Stream additional reference signal v_diffControl upper and lower bridge arm energy and value, using circulation i_diffIn fundametal compoment exchange defeated with described A DC quantity for going out to hold output voltage product to produce controls the difference of upper and lower bridge arm energy；

Control to continue as electric capacity charging by the PR to the energy and value, the control of the energy differences and alternating current, make The capacitance voltage of the capacitance voltage and DC side that obtain submodule reaches rated value, and then system completes start-up course, into stabilization Working condition.

2. it is as claimed in claim 1 to start method, it is characterised in that the step (1) needs to be opened with soft in the starting stage Dynamic resistance, is used to limit the charging current of uncontrollable rectifier stage early stage.

3. it is as claimed in claim 1 or 2 to start method, it is characterised in that the step (2) specifically includes following steps：

1) the energy hole stage one, under the PR control actions of energy hole and alternating current, AC is given simultaneously with DC side Submodule transimission power, now the DC component of circulation is to flow to the submodule by DC side so that the submodule voltage It is rapid to rise so that the submodule capacitor voltage first reaches rated value；

2) the energy hole stage two, AC in power transmission to the submodule, due to the effect of energy hole, the son Module transmits power to DC side so that on the capacitance voltage of the DC side by this carrier of the DC component of circulation Rated value is raised to, now the direction of DC component is to flow to DC bus capacitor from the submodule in circulation.

4. method as claimed in claim 3, it is characterised in that the PR controllers 1) can be realized to sinusoidal quantity without quiet Difference control, controls to may be such that alternating current tracks Setting signal by PR, can ensure in the case where ac grid voltage is constant The energy of AC input rectifier keeps constant, is that rectifier Neutron module electric capacity and DC bus capacitor provide rechargeable energy.

5. method as claimed in claim 3, it is characterised in that the energy hole principle 2) is：

For the single-phase MMC rectifier, the expression formula of each bridge arm gross energy change is：

$\frac{{\mathrm{dW}}_{ap}^{\mathrm{\Σ}}}{dt}=v_{ap}^{ref}{i}_{ap}=(\frac{U_{dc}}{2}-e_j^{ref}-v_{diff})(\frac{i_j}{2}+i_{diff})---\left(1\right)$

$\frac{{\mathrm{dW}}_{an}^{\mathrm{\Σ}}}{dt}=v_{an}^{ref}{i}_{an}=(\frac{U_{dc}}{2}+e_j^{ref}-v_{diff})(-\frac{i_j}{2}+i_{diff})---\left(2\right)$

In formula, W_ap ^∑、W_an ^∑、v_ap ^ref、v_an ^ref、i_ap、i_an、U_dc、e_j ^ref、i_j、i_diff、v_diffRespectively go up bridge arm gross energy, under The gross energy of bridge arm, the bridge arm output reference voltage of upper bridge arm, the bridge arm output reference voltage of lower bridge arm, upper bridge arm current, under Bridge arm current, DC voltage, equivalent AC output reference voltage, alternating current, bridge arm circulation, circulation additional reference signal,

And then the change of the difference of the energy sum and energy of upper and lower bridge arm can be obtained turn to：

$\frac{{\mathrm{dW}}_C^{\mathrm{\Σ}}}{dt}=(U_{dc}-2v_{diff})i_{diff}-e_j^{ref}{i}_j---\left(3\right)$

$\frac{{\mathrm{dW}}_C^{\mathrm{\Δ}}}{dt}=2e_j^{ref}{i}_{diff}-(\frac{U_{dc}}{2}-v_{diff})i_j---\left(4\right)$

W_c ^∑、W_c ^ΔThe difference of upper and lower bridge arm energy sum and energy is represented respectively, and upper and lower bridge is can be seen that by (3) and (4) two formulas The regulation of arm energy sum and circulation additional reference signal v_diffIt is relevant；And the control of the difference of upper and lower bridge arm energy, then can pass through Control i_diffIn fundametal compoment so that its product with ac output voltage produces a DC quantity to go to control the difference of energy Value.