CN104753378A - Three-level inverter midpoint potential balance control method - Google Patents

Abstract

The invention discloses a three-level inverter midpoint potential balance control method. The three-level inverter midpoint potential balance control method comprises the following steps of (1) calculating according to a current adjustor to obtain an instruction voltage and determining a section by a voltage instruction; (2) selecting a vector which is suitable for stabilizing the potential of a midpoint according to positive and negative positions and section positions of three-phase outputting currents Ia, Ib and Ic, the size of a direct-current voltage Udc1 of a capacitor of an upper end, the size of a direct-current voltage Udc2 of a capacitor of a lower end and a vector selection table in the specification; and (3) calculating distributing time of three vectors according to the instruction voltage and the selected vectors, and calculating on-off time of various IGBTs (insulated gate bipolar transistors) according to the distributing time of the vectors so as to obtain driving signals. The three-level inverter midpoint potential balance control method is based on a diode clamping type topological structure, and the vector which is suitable for stabilizing the potential of the midpoint is selected to balance the voltage of the upper capacitor and the voltage of the lower capacitor according to the positive and negative directions and the section positions of the three-phase outputting currents, the size of the direct-current voltage of the capacitor at the upper end and the size of the direct-current voltage of the capacitor at the lower end.

Description

A kind of three-level inverter neutral-point potential balance control method

Technical field

The present invention relates to electric energy Treatment process field, concrete and a kind of three-level inverter neutral-point potential balance control method.

Background technology

Inverter is widely used in industrial production, as frequency conversion equipment, Electric Traction equipment, in order to provide enough power, mostly be two level three-phase inverters, and in some micromanipulators, two level can not meet the demands, many level must be adopted to reduce output harmonic wave, to reduce the shake of control object, common many level topology diode clamp type and flying capacitor type and MMC multi-module cascade, flying capacitor type is because electric capacity number is many, equilibrium problem not easily solves each other, so apply less, and MMC multi-module cascade cost is higher, be more suitable for high pressure occasion, therefore general employing diode clamp type topological structure, the present invention is also optimized improvement for the control method of this topology.

Three-level control principle method is mainly SPWM Carrier wave and SVPWM means of space vector representation, space vector controls to export by Vector modulation, and control precision is high, and therefore means of space vector representation output harmonic wave is lower than Carrier wave, and the utilance of DC side is higher, means of space vector representation is more suitable for requiring high occasion.Because the upper and lower electric capacity of three-level inverter utilizes asymmetric and device loss difference can build up as voltage deviation; cause upper and lower electric capacity Voltage unbalance; because resolution of vectors is based on perfect symmetry model; once disequilibrium respectively participates in the vector no longer coincidence theory decomposed; cause controlling to be deteriorated; output harmonic wave increase, time serious system-down protection, therefore in three-level control principle the most core be midpoint potential balance control.

In order to solve upper and lower electric capacity equilibrium problem, common is at present resistance isostatic pressing and redistribute middle small vector method action time or both dual-purposes.

Resistance isostatic pressing basic thought is to the drain charge of upper and lower side electric capacity by parallel resistance, unloading rate and capacitance voltage are directly proportional, if terminal voltage under upper terminal voltage >, so upper end electric capacity unloading rate > lower end electric capacity unloading rate, two capacitance voltages are carried out along the direction of balance, resistance less balanced action speed is faster, but additionally can increase resistance loss, reduce device efficiency, usual resistance is all selected in more than 10K level, and alignment imbalance plays certain inhibitory action.

Redistribute small vector method action time basic thought be according in, the effect tendency of small vector alignment balance is different, by upper and lower side electric capacity pressure reduction PI obtain an amount trimmed be superimposed upon in, on small vector, the direction that mid-point voltage is tended to be balanced is carried out, the size of amount trimmed is relevant with upper and lower side differential loss degree, amount trimmed can not be excessive, otherwise can affect output vector and, cause export be deteriorated.

Summary of the invention

The object of the invention is to overcome above-mentioned deficiency existing in prior art, a kind of three-level inverter neutral-point potential balance control method is provided, is intended to solve three-level inverter upper and lower electric capacity and utilizes asymmetric and device loss difference can build up as voltage deviation thus cause the problem of upper and lower electric capacity Voltage unbalance.

In order to realize foregoing invention object, the invention provides following technical scheme:

A kind of three-level inverter neutral-point potential balance control method, is characterized in that, comprise the steps: step one: judge sector, voltage place according to inverter voltage instruction, and calculate command voltage through current regulator;

Step 2: select the vector that is applicable to stablizing midpoint potential see following vector option table according to the size of the positive negative direction of electric current of three-phase output current Ia, Ib, Ic, sector position and upper end capacitor direct current voltage Udc1 and lower end capacitor direct current voltage Udc2;

Step 3: according to command voltage and selected vector, calculates the distribution time of three vectors, according to the make-and-break time of each IGBT of vector assignment Time Calculation, calculates drive singal.

In the present invention, the neutral balance provided according to three-level inverter neutral-point potential balance control method controls inverter, comprises auxiliary electric module, acquisition module, inversion control, driver module, power model and load; Inverter controller communicates with auxiliary electric model calling with acquisition module, driver module respectively, and driver module connects driving power module.

Auxiliary electric module: for acquisition module, inverter controller, drive circuit provide reliable and stable power supply;

Acquisition module: the conversion realizing electricity and signal, system carries out closed-loop control according to the feedback quantity gathered;

Driver module and power model: the conversion realizing signal and power.

Compared with prior art, beneficial effect of the present invention:

The present invention is based on diode clamp type topological structure, utilize the positive negative direction of electric current of three-phase output current Ia, Ib, Ic, the size of sector position and upper end capacitor direct current voltage Udc1 and lower end capacitor direct current voltage Udc2 selects the vector being applicable to stablizing midpoint potential to realize the balance of upper and lower capacitance voltage.

Accompanying drawing explanation

Fig. 1 is diode clamp type topology diagram;

Fig. 2 is that neutral balance controls inverter schematic diagram;

Fig. 3 is inverter controller control block diagram;

Fig. 4 is three level Vector modulation figure;

Fig. 5 is the equivalent circuit diagram of PPP zero vector;

Fig. 6 is the equivalent circuit diagram of POO small vector;

Fig. 7 is the equivalent circuit diagram of ONN small vector;

Fig. 8 is the equivalent circuit diagram of PPO small vector;

Fig. 9 is the equivalent circuit diagram of OON small vector;

Figure 10 is the equivalent circuit diagram of vector in PON;

Figure 11 is the equivalent circuit diagram of the large vector of PNN;

The equivalent circuit diagram of the large vector of Figure 12 PPN.

Embodiment

Below in conjunction with test example and concrete/the present invention is described in further detail for execution mode.But this should be interpreted as that the scope of the above-mentioned theme of the present invention is only limitted to following embodiment, all technology realized based on content of the present invention all belong to scope of the present invention.

First, vector definition is done: for A phase

According to Fig. 1 hardware circuit, for A phase, have 4 kinds of states, be described below:

In like manner B, C two-phase is the same with A phase, Uc1=Uc2=Udc, and in following table, UA is the voltage on RA, and UB is the voltage on RB, and UC is the voltage on RC, different vectors, and three-phase output voltage is as follows:

ABC vectorial combination	To the effect of output voltage	Vector defines
			PPP NNN OOO	UA＝0UB＝0UC＝0	Zero vector
PPO OON	UA＝UB＝1/3Udc UC＝-2/3Udc	Small vector

POO ONN	UA＝2/3Udc UB＝UC＝-1/3Udc	Small vector
			PON	UA＝Udc UB＝0UC＝-Udc	Middle vector
PPN	UA＝UB＝2/3Udc UC＝-4/3Udc	Large vector
			PNN	UA＝4/3Udc UB＝UC＝-2/3Udc	Large vector

According to the above, positive vector P is defined as: when A phase insulated gate bipolar transistor IGBT state is G1 conducting, G3 disconnection, G2 conducting, G4 disconnection, A phase exports positive voltage, and A phase current rises; Zero vector O is defined as: when A phase insulated gate bipolar transistor IGBT state is G1 disconnection, G3 conducting, G2 conducting, G4 disconnection, A phase current is by D1 and D2 afterflow; When negative vector N:G1 disconnection, G3 conducting, G2 disconnection, G4 conducting, A phase exports negative voltage, and A phase current declines; In like manner B, C two-phase is the same with A phase, Uc1=Uc2=Udc

Three-phase output voltage: UA is the voltage on RA, and UB is the voltage on RB, and UC is the voltage on RC, zero vector: as UA=0, UB=0, UC=0, the vectorial combination of A phase B phase C phase is: PPP NNNOOO; Small vector: during UA=UB=1/3Udc UC=-2/3Udc, the vectorial combination of A phase B phase C phase is: during PPOOON or UA=2/3Udc UB=UC=-1/3Udc, the vectorial combination of A phase B phase C phase is POOONN; Middle vector: during UA=Udc UB=0 UC=-Udc, the vectorial combination of A phase B phase C phase is PON; Large vector: when the vectorial combination of A phase B phase C phase is PPN or UA=4/3Udc UB=UC=-2/3Udc during UA=UB=2/3Udc UC=-4/3Udc, the vectorial combination of A phase B phase C phase is PNN.

Three level Vector modulation figure is shown in Fig. 4, below analyze with regard to all vector alignment point position influences of first sector:

A) PPP zero vector equivalent circuit Fig. 5, PPP, OOO, NNN are zero level, and output voltage is 0, and three-phase current alignment current potential is without impact

B) POO small vector equivalent circuit Fig. 6, midpoint potential is subject to impact, due to Ia+Ib+Ic=0, be namely subject to impact, as Ia>0, Udc1 discharges, voltage drop; As Ia<0, Udc1 charges, voltage rise.

C) ONN small vector equivalent circuit Fig. 7, midpoint potential is subject to impact, as Ia>0, Udc2 discharge, voltage drop; As Ia<0, Udc2 charges, voltage rise

D) PPO small vector equivalent circuit Fig. 8, midpoint potential is subject to impact, as Ic>0, Udc2 discharge, voltage drop; As Ic<0, Udc2 charges, voltage rise

E) OON small vector equivalent circuit Fig. 9, midpoint potential is subject to impact, due to Ia+Ib+Ic=0, be namely subject to impact, as Ic>0, Udc2 charges, voltage rise; As Ic<0, Udc2 discharges, voltage drop

F) vector equivalent circuit Figure 10 in PON, midpoint potential is subject to impact, as Ib>0, center line output current, Udc1 rise, Udc2 decline; The center line input current as Ib<0, Udc1 declines, and Udc2 rises.

G) large vector equivalent circuit Figure 11 of PNN, mid point is without any connection, unaffected

H) large vector equivalent circuit Figure 12 of PPN, mid point is without any connection, unaffected

Following table is drawn after gathering:

Table 1 current potential and vector, function of current relation

Can draw from analysis above, control mid point level and can carry out appropriate control by current direction alignment current potential, small vector and middle vector alignment current potential is wherein only had to impact, therefore can according to upper and lower side electric capacity pressure reduction and current direction select suitable in small vector synthesize, in order to reduce output ripple during selection, only has a switch change during vectors switching for best.

Such as little sector, sector 1, can by 4 kinds of vectorial combinations

Zero vector+PPO or OON+POO or ONN combines, and according to the interactively of such as following table, selects the vector being conducive to potential balance

Claims (2)

1. a three-level inverter neutral-point potential balance control method, is characterized in that, comprises the steps:

Step one: judge sector, voltage place according to inverter voltage instruction, and calculate command voltage through current regulator;

Step 2: select the vector that is applicable to stablizing midpoint potential see following vector option table according to the size of the positive negative direction of electric current of three-phase output current Ia, Ib, Ic, sector position and upper end capacitor direct current voltage Udc1 and lower end capacitor direct current voltage Udc2;

Step 3: according to command voltage and selected vector, calculates the distribution time of three vectors, according to the make-and-break time of each IGBT of vector assignment Time Calculation, calculates drive singal.

2. neutral balance controls an inverter, it is characterized in that, comprises auxiliary electric module, acquisition module, inversion control, driver module, power model and load; Inverter controller communicates with auxiliary electric model calling with acquisition module, driver module respectively, and driver module connects driving power module;

Auxiliary electric module: for acquisition module, inverter controller, drive circuit provide reliable and stable power supply;

Acquisition module: the conversion realizing electricity and signal, system carries out closed-loop control according to the feedback quantity gathered;

Driver module and power model: the conversion realizing signal and power.