CN110086361A - A kind of five single-phase phase-deficient operation control methods of phase current source type current transformer - Google Patents

Abstract

The invention discloses a single-phase lack-of-phase operation control method for a five-phase current source type converter, which includes the following steps: Step S1: Set the phase voltage vectors of the remaining non-faulty four phases Decompose the sequence components to obtain the vector set of phase voltage sequence components of the non-faulty four phases The output of the PI controller is defined as the constant active power reference value P _ref of the converter; Step S2: Calculate the line current reference value vector set of the non-faulty four phases of the converter Step S3: According to the set of phase voltage sequence component vectors of the non-faulty four phases And the filter capacitor capacitance C _f is calculated to obtain the filter capacitor compensation current vector set Step S4: will get and Adding to obtain the vector set of the reference value of the converter modulation current Obtain the duty cycle signal of the switch tube corresponding to the non-fault through SPWM modulation; Step S5: Obtain the duty cycle signal of the switch tube, thereby controlling the on and off of the switch tube of the converter.

Description

A control method for single-phase lack of phase operation of a five-phase current source converter

technical field

The invention relates to a control method of a five-phase current source type converter in a five-phase independent power grid, in particular to a control method for single-phase lack of phase operation of a five-phase current source type converter.

Background technique

In the fields of new-type locomotive traction, mine hoisting, and ship propulsion, the demand for transmission power of drive converters continues to increase. At present, a solution with good application prospects is to use five-phase current source converters to transmit power.

Compared with the traditional three-phase current source system, the five-phase current source system, as a promising solution for low-voltage and high-power applications, has the following significant advantages:

(1) Using switching devices of the same power level, the five-phase current source system can realize low-voltage high-power conversion, and the voltage stress borne by each phase switching device is significantly reduced.

(2) When the five-phase current source converter is applied to drive a five-phase motor, the torque output density is high, the pulsation frequency is increased, and the pulsation amplitude is reduced, which can improve the operating efficiency of the motor.

(3) It has better fault tolerance and high operational reliability. Because there is redundancy in the number of phases in the five-phase current source system, when one or several phases of the five-phase variable current source converter fail, reasonable control methods can still be used to make the converter continue to run with derated power No downtime required. In addition, in the event of a short circuit fault, due to the current limiting effect of the DC side inductance, it can still run continuously for a period of time.

(4) There are many degrees of control freedom and high flexibility. The controllable degree of freedom of the five-phase current source converter is equal to the number of independent phases, so it has higher control flexibility and can achieve more control performance.

Among them, the most prominent advantage of the five-phase current source converter in practical applications is its high operational reliability, which can realize reliable operation under short circuit and phase loss conditions. In the case of a short circuit, due to the existence of the DC side inductance, the rapid increase of the short circuit current is limited, and the current source converter still works in the normal constant current mode in a short period of time, which avoids the harm of the converter due to excessive current. In the case of lack of phase operation, due to the asymmetric power supply of the converter, the traditional control method will lead to an increase in the secondary ripple of the DC bus current, an increase in the peak value of the AC side line current, and severe waveform distortion. However, no related method has been proposed for the phase-deficient operation of the five-phase current source converter.

SUMMARY OF THE INVENTION

The purpose of the present invention is to fill the gap in the prior art and provide a control method for single-phase phase-lack operation of a five-phase current source type converter in a five-phase independent grid. The method can ensure that the instantaneous active power fluctuation is zero while the current amplitude of the AC side line is minimized when the five-phase current source converter transmits constant power. The operation reliability of the five-phase current source converter is significantly improved, and the system has the ability to continue to operate without shutting down in the event of a single-phase open-phase fault.

The purpose of the present invention is achieved through the following technical solutions:

A five-phase current source type converter single-phase lack of operation control method, based on the grid-connected rectifier of the five-phase current source type converter, the five-phase current source type converter is connected to the common connection point PCC through a filter and then connected to the common connection point PCC The five-phase independent grid exchanges power; among them, the converter consists of ten power switch modules to form a five-phase full-bridge topology, and the DC side of the converter is connected in series with the common DC-side bus inductance L _dc to suppress the current fluctuation of the DC side; The control method includes the following steps:

Step S1: At the beginning of each switching cycle, the converter uses the sampling circuit to collect the phase voltage vector sets of the remaining non-faulty four phases and the DC bus current i _dc , and the and i _dc are sent to the control module of the converter, Decompose the sequence components to obtain the vector set of phase voltage sequence components of the non-faulty four phases I _dc is processed by digital low-pass filtering to obtain i _{dc_LPF} , and the difference between the preset DC bus current reference value i _{dc_ref} and i _{dc_LPF} is used as the input of the PI controller, and the output of the PI controller is defined as the constant active power of the converter Reference value P _ref ;

Step S2: Use the phase voltage sequence component vector set of the non-faulty four phases obtained in step S1 and the constant active power reference value P _ref to obtain the line current reference value vector set of the non-faulty four phases of the converter

Step S3: According to the set of phase voltage sequence component vectors of the non-faulty four phases And the filter capacitor capacitance C _f is calculated to obtain the filter capacitor compensation current vector set

Step S4: will get and Adding to obtain the vector set of the reference value of the converter modulation current Obtain the duty cycle signal of the non-fault corresponding switch tube through SPWM modulation;

Step S5: Obtain the duty cycle signal of the switching tube, thereby controlling the switching on and off of the switching tube of the converter.

Further, step S1 includes performing sequence component decomposition on the phase voltages of the four non-faulty phases. The fault circuit is equivalent to a four-phase asymmetrical circuit through circuit analysis, and then the sequence components of the four-phase voltage and current are obtained by using the symmetrical component method.

Further, step S2 includes a calculation algorithm of the line current reference value vector set. The reference value of the instantaneous active power of the system is obtained through the DC bus current regulator, and then the set of line current reference vectors is calculated by using each sequence component of the four-phase voltage.

Further, step S4 includes a modulation method of the asymmetrical four-phase current. The bipolar carrier is compared with the four-phase current reference to obtain the conduction time corresponding to each phase switch.

Compared with the prior art, the beneficial effects brought by the technical solution of the present invention are:

1. In the present invention, the symmetrical component method is adopted to decompose the AC voltage in the case of a single-phase phase loss in the five-phase current source system, and five phases are obtained when the fluctuation of the instantaneous active power of the system is zero and the amplitude of the AC current is minimum. The modulation current of the current source converter is referenced and modulated. This makes the five-phase current source converter capable of continuous operation in the case of single-phase phase loss, reduces the electrical impact and noise of the converter in the event of a fault, and can maximize the service life of the converter.

2. This method suppresses the fluctuation of the DC bus current of the converter; under the condition of constant transmission power, minimizes the amplitude of the AC side line current of the converter, reduces the possibility of protection action caused by the current exceeding the limit, and maximizes the Power transfer under fault conditions. At the same time, the power quality of the AC side line current is improved, and the investment and use of additional power quality control devices are reduced.

Description of drawings

Fig. 1-1 is a topological structure of a five-phase current source type converter in which a single-phase phase loss occurs in a specific embodiment of the present invention.

Fig. 1-2 is a control scheme of a five-phase current source type converter in which a single-phase phase loss occurs in a specific embodiment of the present invention.

Fig. 2 is a schematic diagram of time vector distribution of voltage sequence components of a five-phase current source type converter with e-phase lack of phase in the present invention.

Fig. 3 is a schematic diagram of distribution of active and reactive components of voltage and current vector sequence components in the present invention.

Figure 4-1 is a schematic diagram of current waveforms on the AC and DC sides of a five-phase current source converter with e-phase lack of phase when the traditional scheme is applied.

Fig. 4-2 is a schematic diagram of current waveforms on the AC and DC sides of a five-phase current source converter with e-phase lack of phase when the present invention is applied.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The control method of the present invention is based on the topological structure of the five-phase current source type converter grid-connected rectifier in the case of single-phase phase loss as shown in Figure 1-1, and the control method in the case of single-phase phase loss in any one phase is the same Same and as shown in Figure 1-2. Therefore, the control scheme of the present invention will be described in detail by taking the single-phase open-phase fault of the e-phase of the five-phase current source converter as an example. As shown in Figure 1-1, its main circuit structure is as follows: After a five-phase current source converter has an e-phase single-phase phase loss fault, the entire system degenerates into a four-phase current source converter system. The current source converter exchanges power with the four-phase asymmetric independent grid through the CL filter; where R _s is the equivalent internal resistance of the grid, and the four-phase current source converter consists of eight power switch modules to form a four-phase full bridge Topology, the DC side of the four-phase current source converter is connected in series with the common DC side bus inductance L _dc to suppress the current fluctuation of the DC side.

The present invention is a single-phase lack-of-phase operation control method of a five-phase current source type converter, and the specific method is as follows:

Step S1: At the beginning of each switching cycle, the converter uses the sampling circuit to collect the phase voltage vector sets of the remaining non-faulty four phases and the DC bus current i _dc , and the and i _dc are sent to the control module of the converter, Decompose the sequence components to obtain the vector set of phase voltage sequence components of the non-faulty four phases Then, i _dc is processed by digital low-pass filtering to obtain i _{dc_LPF} , and the difference between the preset DC bus current reference value i _{dc_ref} and i _{dc_LPF} is used as the input of the PI controller, and the output of the PI controller is defined as the constant value of the converter Active power reference value P _ref ;

Step S2: Use the phase voltage sequence component vector set of the non-faulty four phases obtained in the previous step and the constant active power reference value P _ref to obtain the line current reference value vector set of the non-faulty four phases of the converter

Step S3: According to the set of phase voltage sequence component vectors of the non-faulty four phases And the filter capacitor capacitance C _f is calculated to obtain the filter capacitor compensation current vector set

Step S4: Will get and Adding to obtain the vector set of the reference value of the converter modulation current The duty ratio signal of the non-fault corresponding switch tube is obtained through SPWM modulation;

Step S5: Obtain the duty cycle signal of the switching tube, thereby controlling the switching on and off of the switching tube of the converter.

The following is a more specific embodiment of the present invention:

In step S1: For the asymmetrical four-phase system shown in Figure 1-1, the supply voltage can be expressed as:

where the voltage vector Among them, v _ga , v _gb , v _gc , and v _gd respectively represent the instantaneous value of each phase voltage, and the amplitude is E. Among them, "+,""-,""00," and "0," represent positive sequence, negative sequence, semi-zero sequence and zero sequence voltage vectors, respectively. Similarly, the AC side line current can also be expressed as:

where the current vector Among them, i _La , i _Lb , i _Lc , i _Ld represent the instantaneous value of each phase line current respectively. The current vector of each sequence component

Here, phase a is taken as an example, and the calculation method of each sequence component is illustrated by using polyphase Fortescue transformation:

The instantaneous value of the phase voltage sequence component of phase a of the asymmetrical system can be obtained from formula (3):

In the same way, the instantaneous values of phase voltage sequence components of phase b, c and d can be obtained. The four-phase voltage sequence components are expressed in the form of time vector as Figure 2.

In step S2: Based on step S1, it can be known that the instantaneous active and reactive power of the converter can be expressed as:

In the formula, p _ins and q _ins refer to the instantaneous active and reactive power of the current source converter respectively. The operator "·" represents the dot product of vectors, and the subscript "⊥" represents the virtual vector used for reactive power calculation, and are orthogonal to each other and have equal magnitudes. As shown in Figure 3, Lags behind Lags behind Lags behind

According to the characteristics of the sequence components of the four-phase system, formula (5) can be simplified as:

In the formula, P ⁺ , P ^- and P ⁰⁰ respectively represent the positive sequence, negative sequence and semi-zero sequence components of constant active power; Q ⁺ , Q ^- and Q ⁰⁰ represent the positive sequence, negative sequence and semi-zero sequence of constant reactive power sequence component; p _2ω and q _2ω represent the double frequency components of active power and reactive power, respectively.

Because there is no zero-sequence current component in the fault system, the constant active power (P _dc ) and reactive power (Q _dc ) transmitted by the converter are defined here as:

In order to eliminate the double-frequency active power fluctuation of the system (that is, p _2ω =0 in formula (6), it needs to meet:

Further simplification to obtain the relational expression of the line current space vector is:

In the formula and respectively represent the active and reactive components of the positive sequence component of the line current vector; and respectively represent the active and reactive components of the negative sequence component of the line current vector; and Represent the active and reactive components of the line current vector semi-zero-sequence component, respectively. The operator "||·||" denotes the modulus of a vector.

From this, the modulus relation of each sequence component of the line current space vector can be obtained as:

Using the relationship between the line current time vector and the system voltage vector obtained by formula (9) and the modulo expression of each sequence component time vector of line current obtained by formula (10), the amplitude expression of the asymmetric four-phase line current can be obtained Mode:

In the formula and represent the amplitudes of the four-phase line currents, which can be regarded as functions of three variables (P ⁰⁰ , Q _dc and Q ⁰⁰ ):

M _iL ＝f(P ⁰⁰ ,Q _dc ,Q ⁰⁰ ) (12)

In the formula

Calculated by the control variable method, on the basis that the instantaneous active power fluctuation of the system is zero and the maximum value of the four-phase line current amplitude is the lowest, the space vector set of the line current reference value sequence components of the non-faulty four-phase converter can be Expressed as:

In step S3: Neglecting the voltage drop on the filter inductor, the capacitor current is:

In the formula and are the positive sequence, negative sequence and semi-zero sequence components of the capacitor current on the filter, respectively. C _f is the capacitance value of the single-phase capacitor of the filter, j indicates that the phase of the capacitor current is ahead of the phase of the voltage across the capacitor by π/2, and ω indicates the angular frequency of the fundamental component of the capacitor current.

In step S4: the reference vector of the output current of the converter is:

In the formula and are the positive sequence, negative sequence, semi-zero sequence and zero sequence components of the converter output current reference vector, respectively.

According to Figure 4-1, it can be seen that when the five-phase current source converter adopts the traditional control scheme, the average value of the DC bus current is 11A, but there is a secondary ripple of about 10A. In addition, the distortion of the current waveform of the AC side line is also very serious, and the amplitudes of the remaining four-phase currents are not equal, and the peak-to-peak value reaches 17A. According to Figure 4-2, it can be seen that when the fault system adopts the control scheme proposed by the present invention, the average value of the DC bus current is still controlled to about 11A, but the DC ripple current is suppressed to 1.5A. The line current waveforms of the remaining four phases have a higher sine degree and equal amplitude, and the peak-to-peak value of the line current is reduced to 12A.

To sum up: the single-phase phase-loss operation control method of the five-phase current source type converter proposed by the present invention can be conveniently applied to the five-phase PWM current source type converter. It has good DC current ripple and AC current peak suppression effect, and is a new converter control method worth popularizing.

The present invention is not limited to the embodiments described above. The above description of the specific embodiments is intended to describe and illustrate the technical solution of the present invention, and the above specific embodiments are only illustrative and not restrictive. Without departing from the gist of the present invention and the scope of protection of the claims, those skilled in the art can also make many specific changes under the inspiration of the present invention, and these all belong to the protection scope of the present invention.

Claims (4)

1. a kind of five single-phase phase-deficient operation control methods of phase current source type current transformer, grid-connected whole based on five phase current source type current transformers Device is flowed, five phase current source type current transformers are connected to after points of common connection PCC by filter and exchange power with five phase isolated power networks； Wherein, current transformer forms five phase full-bridge topologies, the common DC side of DC side series connection of current transformer by ten power switching modules Bus inductance L_dcFor inhibiting the current fluctuation of DC side；It is characterized in that, the control method the following steps are included:

Step S1: when each switch periods start, current transformer acquires the phase voltage of four phase of remaining non-faulting using sample circuit Set of vectorsAnd DC bus current i_dc, and willAnd i_dcIt is sent to the control module of current transformer,Carry out order components point Solution, obtains the phase voltage order components set of vectors of four phase of non-faultingBy i_dcIt handles to obtain through digital low-pass filtering i_{dc_LPF}, by preset DC bus current reference value i_{dc_ref}With i_{dc_LPF}Input of the difference as PI controller, PI controller Output is defined as the constant active power reference value P of current transformer_ref；

Step S2: using the phase voltage order components set of vectors of obtained four phase of non-faulting of step S1With constant wattful power Rate reference value P_refThe line current reference value set of vectors of four phase of current transformer non-faulting is calculated

Step S3: according to the phase voltage order components set of vectors of four phase of non-faultingAnd filter capacity capacitance C_fIt calculates Obtain filter capacitor compensation current phasor set

Step S4: by what is obtainedWithAddition obtains current transformer modulation current reference value set of vectorsPass through SPWM tune The duty cycle signals of the corresponding switching tube of non-faulting are made；

Step S5: obtaining the duty cycle signals of switching tube, thus controls opening and turning off for converter switches pipe.

2. a kind of five single-phase phase-deficient operation control methods of phase current source type current transformer according to claim 1, which is characterized in that Order components decomposition is carried out comprising the phase voltage to four phase of non-faulting in step S1；Specifically by analysis circuit by faulty circuit etc. Effect is four phase unsymmetric circuits, obtains each order components of four phase voltages, electric current using symmetrical component method later.

3. a kind of five single-phase phase-deficient operation control methods of phase current source type current transformer according to claim 1, which is characterized in that Include the computational algorithm of line current reference value set of vectors in step S2, obtains system especially by DC bus current adjuster The set of line current reference vector is calculated in the reference value of instantaneous active power using each order components of four phase voltages later.

4. a kind of five single-phase phase-deficient operation control methods of phase current source type current transformer according to claim 1, which is characterized in that Modulator approach comprising asymmetric four phase currents in step S4, specially does ratio using bipolarity carrier wave and four phase-current references Compared with respectively obtaining the corresponding turn-on time of every phase switching tube.