Controllable phase shifter control method based on power compensation and phase compensation

Abstract

The invention provides a control method of a controllable phase shifter based on power compensation and phase compensation, and the method comprises the steps: setting a CHBC capacitor voltage reference value and a line power reference value, and obtaining a line power actual value and a CHBC capacitor voltage; calculating a q-axis component reference value of the CHBC output current by using a power compensation control method; calculating a d-axis component reference value of the CHBC output current by using an overall voltage balance control method; respectively obtaining reference values of d-axis and q-axis components of CHBC output voltage by adopting current control, and performing phase compensation to obtain a three-phase modulation wave I; obtaining a three-phase modulation wave II by using an inter-phase voltage balance control method; obtaining a three-phase modulation wave III by using an in-phase voltage balance control method; modulation waves are converted into CHBC internal switch tube signals through the bipolar carrier phase-shifting PWM technology, and control over output voltage is achieved. According to the invention, the continuous adjustment of the phase shift angle of the HPFC can be realized, and the indifference adjustment of the active power of the line and the balance and stability of the internal capacitor voltage of the CHBC can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a control method of a phase shifter. Background Art

[0002] As the most typical FACTS device, the unified power flow controller (UPFC) has good effects in power flow regulation and load balancing. However, due to the large-scale use of high-power power electronic devices, the topology of UPFC is relatively complex, the cost is high, and the floor space requirement is large. In contrast, the hybrid power flow controller (HPFC) combined with the cascaded H-bridge converter (CHBC) is a new type of flexible AC power transmission equipment with a simpler structure and higher economy. It not only has the function of regulating the power flow of the power grid and improving the power distribution of the system like the traditional mechanical controllable phase shifter, but also overcomes the problem of dead zone in the traditional mechanical controllable phase shifter, and has the characteristics of continuous regulation.

[0003] The invention patent with publication number CN102522906A discloses a voltage balance and power balance control method for a cascaded H-bridge converter, which discloses the following steps: (1) dual closed-loop control, used to provide the same modulation wave vector to each H-bridge; (2) voltage balance control; (3) power balance control; the voltage balance control and power balance control respectively improve the modulation wave vector to obtain a reconstructed modulation wave vector as the modulation signal of each H-bridge. The present invention does not need to add additional circuits. This method not only keeps the DC side voltage of each H-bridge balanced and the voltage ripple basically consistent, but also allows the active power flowing through each H-bridge to be distributed on demand and the reactive power to be distributed equally. However, this method is difficult to automatically adjust the CHBC compensation voltage to meet the line power demand.

[0004] At present, cascaded H-bridge converters are mainly used in reactive power compensation devices such as static synchronous compensators STATCOM, and there are relatively mature control methods, such as reactive current compensation control and capacitor voltage balancing control. However, since the main function of the CHBC cascaded H-bridge converter in HPFC is to provide compensation voltage to achieve continuous and error-free adjustment of the phase shift angle, rather than to compensate reactive power to the power grid, if the CHBC is to automatically adjust the amplitude and phase of the compensation voltage according to the line power demand and achieve error-free adjustment of the line power, it is necessary to improve the control strategy. Summary of the invention

[0005] In view of the technical problem that the existing methods are difficult to automatically adjust the CHBC compensation voltage to meet the line power demand, the present invention proposes a control method for a controllable phase shifter based on power compensation and phase compensation. The power compensation control method, the three-layer voltage equalization control method and the phase compensation method are used to realize continuous adjustment of the HPFC phase shift angle, thereby realizing the difference-free adjustment of the line active power and the balanced and stable voltage of the CHBC internal capacitor.

[0006] In order to achieve the above object, the technical solution of the present invention is achieved as follows:

[0007] A control method for a controllable phase shifter based on power compensation and phase compensation, characterized in that it comprises the steps of:

[0008] S1: Set the CHBC capacitor voltage reference value and line power reference value, and obtain the actual line power value and CHBC capacitor voltage;

[0009] S2: Calculate the q-axis component reference value of the CHBC output current by using the power compensation control method based on the line power reference value and the line power actual value; Calculate the d-axis component reference value of the CHBC output current by using the overall voltage balancing control method based on the CHBC capacitor voltage reference value and the average value of the CHBC overall capacitor voltage;

[0010] S3: Based on the q-axis component reference value of the CHBC output current and the d-axis component reference value of the CHBC output current, current control is used to obtain the reference values ​​of the d-axis and q-axis components of the CHBC output voltage respectively and phase compensation is performed to obtain a three-phase modulation wave I;

[0011] S4: Based on the average value of the CHBC phase capacitor voltage and the average value of the CHBC overall capacitor voltage, a three-phase modulation wave II is obtained by using a phase voltage balancing control method;

[0012] S5: Based on the voltage of each capacitor in the CHBC phase and the average value of the capacitor voltage in the CHBC phase, a three-phase modulation wave III is obtained by using an intra-phase voltage balancing control method;

[0013] S6: Superimpose three-phase modulation wave I, three-phase modulation wave II and three-phase modulation wave III and use bipolar carrier phase-shift PWM technology to convert the superimposed modulation wave into a CHBC internal switch tube signal to control the output voltage amplitude and phase of the H-bridge commutation unit.

[0014] The power compensation control method in step S2 is:

[0015] Calculate the actual value of line power P line With the reference active power value P ref The difference is used as input to perform PI control calculation, and the output of the PI control calculation is used as the reference value I of the q-axis component of the CHBC output current.cq_ref ;

[0016] The PI control calculation formula is:

[0017]

[0018] in, is the proportional adjustment coefficient of the q-axis PI control, is the integral adjustment coefficient of q-axis PI control, and S is the Laplace operator.

[0019] The overall voltage balance control method in step S2 is: calculating the average value U of the overall capacitor voltage of CHBC dc_ref , the CHBC capacitor voltage reference value U dc_ref The average value of the total capacitance voltage of CHBC is U dc_ave The total capacitance error is obtained by subtracting the total capacitance error, and the PI control calculation is performed with the total capacitance error as input. The output of the PI control calculation is used as the d-axis component reference value I of the CHBC output current. cd_ref .

[0020] The phase compensation method is as follows: taking the primary side voltage phase of the parallel transformer as a reference, obtaining a reference value calculation formula for the CHBC output voltage, obtaining a phase difference δ of the CHBC output voltage relative to the primary side voltage of the parallel transformer and a phase difference α of the CHBC output current relative to the primary side current of the parallel transformer according to the reference value calculation formula for the CHBC output voltage; calculating a compensation phase angle according to the phase difference δ and the phase difference α, using the compensation phase angle as a rotation angle to perform an inverse Park transformation on the reference values ​​of the d-axis and q-axis components of the CHBC output voltage, and obtaining a three-phase modulation wave I.

[0021] The reference value calculation formula of the CHBC output voltage is:

[0022]

[0023] in, is the reference value of CHBC output voltage, is the reference value of the CHBC output voltage, is the amplitude of the reference value of the CHBC output current, R is the CHBC equivalent resistance, L is the filter inductance, ω is the angular frequency, and j is the imaginary unit.

[0024] The compensation phase angle is:

[0025]

[0026] in, is the primary side voltage phase angle of the parallel transformer, U rd1 is the reference value of the d-axis component of the CHBC output voltage, Urq1 It is the reference value of the q-axis component of the CHBC output voltage.

[0027] The phase-to-phase voltage balancing control method is as follows: the difference between the average value of the CHBC phase capacitor voltage of each phase and the average value of the overall capacitor voltage of the three-phase CHBC is calculated, and the difference between the CHBC current of each phase and the d-axis component of the CHBC output current is obtained through the proportional link K2, and then the compensation voltage amplitude of each phase is obtained through the proportional link K1, and finally multiplied with the corresponding sinusoidal function to obtain the three-phase modulation wave II.

[0028] The intra-phase voltage balancing control method is as follows: the difference between the average value of the phase capacitor voltage of each phase CHBC and the voltage of each capacitor in the phase is calculated, and the compensation voltage amplitude of each phase CHBC used to compensate for the pulse delay is obtained through the proportional link K3, and finally the q-axis component of the output current of each phase CHBC and the corresponding cosine function are multiplied to obtain the three-phase modulation wave III.

[0029] The method for obtaining the reference values ​​of the d-axis and q-axis components of the CHBC output voltage is as follows: the CHBC output current is subjected to park transformation with the primary side voltage phase of the excitation transformer as the rotation angular frequency to obtain the d-axis component I of the CHBC output current. cd and the q-axis component I cq ; The d-axis component I of the CHBC output current is cd and the d-axis component reference value I of the CHBC output current cd_ref As input, the q-axis component of the CHBC output current I cq and the q-axis component reference value I of the CHBC output current cq_ref As input, the d-axis component I of the CHBC overall output current is controlled by a feedforward decoupling control strategy. cd and the q-axis component I cq Feedforward decoupling is performed to obtain the reference value U of the d-axis component of the CHBC output voltage rd1 and the reference value U of the q-axis component rq1 .

[0030] The CHBC includes three working states, including a compensation state, a cut-out state and a locking state.

[0031] Beneficial effects of the present invention: the power compensation control method compensates for the voltage dead zone of the secondary side of the parallel transformer by controlling the reference value of the q-axis component of the output voltage of the CHBC to achieve continuous regulation of the active power of the line; the three-layer uniform control method aims to control the voltage balance and stability of each capacitor inside the three-phase CHBC; the phase compensation method aims to control the output voltage of the CHBC to be consistent with the phase of the primary side voltage of the excitation transformer. The combination of the three makes the entire power transmission process smoother and more reliable, improves the stability of the system, not only improves its own operating efficiency and reliability, but also has a positive effect on improving the quality of the entire power network. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 The invention is a control block diagram of a controllable phase shifter control method.

[0034] Figure 2 It is a topology diagram of a controllable phase shifter combined with a cascaded H-bridge converter.

[0035] Figure 3 It is a simple power supply ring network.

[0036] Figure 4 (a) is the single-phase equivalent circuit of HPFC, and (b) is the single-phase equivalent circuit of CHBC.

[0037] Figure 5 2 is a simulation circuit diagram of an embodiment.

[0038] Figure 6 is the active power flowing through the HPFC.

[0039] Figure 7 is the CHBC output voltage.

[0040] Figure 8 is the CHBC output current.

[0041] Fig. 9 is the average capacitor voltage of each phase. DETAILED DESCRIPTION

[0042] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] like Figure 1 As shown, the HPFC includes a series transformer, a shunt transformer and a CHBC. After the HPFC is connected to the system, the primary side of the shunt transformer obtains voltage from the power grid through the series transformer. The secondary side is equipped with a tap switch shunt transformer to perform coarse power adjustment to generate an adjustable secondary voltage. Then, the PWM controller performs comprehensive control on the CHBC, and combines it with the adjustable secondary voltage to generate a phase-shifted voltage with adjustable phase and amplitude. Through circuit connection, the phase-shifted voltage is compensated to the primary side of the series transformer, and then compensated to the power grid.

[0044] The CHBC is composed of multiple groups of H-bridge commutation units connected in series, such as Figure 2 As shown, each H-bridge commutation unit includes four IGBT switch tubes (first to fourth switch tubes) equipped with reverse parallel freewheeling diodes and a DC capacitor. The first switch tube and the second switch tube constitute the left bridge arm, and the third switch tube and the fourth switch tube constitute the right bridge arm. The four switch tubes are in the same forward conduction direction, and the forward conduction direction of the freewheeling diode is opposite to that of the switch tube. The two bridge arms are connected in parallel with the DC capacitor, and the lines are led out from the common points of the switch tubes of each bridge arm and connected to the external circuit. The gate of the switch tube is connected to the external PWM control circuit, and the bipolar carrier phase-shifted PWM technology commonly used in the cascaded H-bridge converter is used to convert the modulation signal into the CHBC internal switch tube signal to control the output voltage amplitude and phase of the H-bridge commutation unit.

[0045] According to the HPFC, this embodiment describes in detail the method of the present invention, a control method of a controllable phase shifter based on power compensation and phase compensation, such as Figure 1 As shown, the steps are:

[0046] S1: Set the CHBC capacitor voltage reference value and the line power reference value, and obtain the actual line power value and the CHBC capacitor voltage.

[0047] In this embodiment, the HPFC is installed in a 220 kV line, the line power target connected to the HPFC is set to 118 MW, and the reference value of the capacitor voltage in each H-bridge converter unit in the CHBC of the A, B, and C phases is set to U dc_ref , in this embodiment, the capacitor voltage reference value is 0.8kV.

[0048] S2: Calculate the q-axis component reference value of the CHBC output current using the power compensation control method based on the line power reference value and the line power actual value; calculate the d-axis component reference value of the CHBC output current using the overall voltage balancing control method based on the CHBC capacitor voltage reference value and the CHBC overall capacitor voltage average value.

[0049] The CHBC output current is the overall output current of n H-bridge commutation units inside each phase CHBC.

[0050] Power compensation control method:

[0051] by Figure 3 The ring network circuit shown is as follows: S is the input line voltage, is the phase shift angle of HPFC, U1 is the line voltage at the HPFC outlet, Z1 and Z2 are line 1 and line 2 impedances respectively, and the line resistance is ignored. The circulating power S in the network can be calculated. C for:

[0052]

[0053] Among them, U N represents the rated voltage of the HPFC system, and X1 and X2 represent the reactance of lines 1 and 2.

[0054] Due to the phase shift angle of HPFC Generally small, so the cycle power S C The reactive component in can be ignored, and the phase shift angle of HPFC With cycle power S C Approximately satisfies the linear relationship.

[0055] Further, according to the single-phase equivalent circuit of HPFC, Figure 4 As shown, the phase shift angle of HPFC can be calculated The output voltage amplitude K of CHBC H The mathematical relationship is:

[0056]

[0057] Among them, n T is the parallel transformer ratio, n B is the series transformer ratio, Indicates the primary side voltage amplitude of the parallel transformer.

[0058] Due to the phase shift angle of HPFC Generally small, and the polynomial in the inverse tangent function is about the output voltage amplitude K of CHBC H is a linear function, so the phase shift angle of HPFC The output voltage amplitude K of CHBCH Approximately satisfies the linear relationship.

[0059] Therefore, the output voltage amplitude K of CHBC can be obtained H With cycle power S C Approximately satisfies the linear relationship.

[0060] The output voltage of CHBC acts on the secondary winding of the series transformer through the circuit connection and is coupled to the line, changing the phase difference of the voltage on both sides of the controllable phase shifter, that is, the phase shift angle By changing the phase shift angle, the circulating power can be changed, and the actual power in the line is equal to the circulating power plus the natural power (the active power in the line before the controllable phase shifter is installed).

[0061] Therefore, the proportional integral (PI) control calculation is introduced, the actual value of the line power is obtained through power measurement, the difference between the actual value of the line power and the reference active power value is calculated, and the PI control calculation is performed, and the output of the PI control calculation is used as the reference value of the q-axis component of the CHBC output current to achieve fine-tuning of the line active power;

[0062]

[0063] in, is the proportional adjustment coefficient of the q-axis PI control, is the integral adjustment coefficient of the q-axis PI control, S represents the Laplace operator, P ref is the line power reference value, P line Actual value of line power.

[0064] Since the output voltage of CHBC is continuously adjustable, the line active power can be continuously regulated without difference by adjusting the q-axis component of the CHBC output current (obtained by park transformation), thus overcoming the problem of power regulation dead zone caused by adjusting the secondary side tap switch of the parallel transformer alone.

[0065] Overall voltage balance control method:

[0066] The d-axis component of the CHBC output current (obtained by park transformation) determines the size of the active power received by the CHBC, and the active power affects the capacitor voltage value inside each stage of the cascaded H-bridge converter. Therefore, by controlling the d-axis component of the CHBC output current, the overall balance of the capacitor voltage value inside each stage of the cascaded H-bridge converter can be achieved.

[0067] Since the d-axis component of the output current of the CHBC is directly related to its input and output active power, a PI control calculation is introduced.

[0068] The overall capacitance error is obtained by subtracting the reference value of the CHBC capacitor voltage from the average value of the CHBC overall capacitance voltage. The overall capacitance error is used as input for PI control calculation. The output of the PI control calculation is used as the reference value of the d-axis component of the CHBC output current to achieve CHBC overall voltage balance:

[0069]

[0070] in, is the proportional adjustment coefficient of the d-axis PI control, is the integral adjustment coefficient of the d-axis PI control, U dc_ref is the reference value of CHBC capacitor voltage, U dc_ave is the average value of the overall capacitance voltage of CHBC.

[0071] S3: Based on the q-axis component reference value of the CHBC output current and the d-axis component reference value of the CHBC output current, current control is used to obtain the reference values ​​of the d-axis and q-axis components of the CHBC output voltage respectively and phase compensation is performed to obtain the three-phase modulation wave I.

[0072] The CHBC output current is park transformed with the primary side voltage phase of the excitation transformer as the rotation angular frequency to obtain the d-axis component I of the CHBC output current. cd and the q-axis component I cq ; The d-axis component I of the CHBC output current is cd and the d-axis component reference value I of the CHBC output current cd_ref As input, the q-axis component of the CHBC output current I cq and the q-axis component reference value I of the CHBC output current cq_ref As input, the d-axis component I of the CHBC overall output current is calculated using a feedforward decoupling control strategy (current control). cd and the q-axis component I cq Feedforward decoupling is performed to obtain the reference value U of the d-axis component of the CHBC output voltage rd1 and the reference value U of the q-axis component rq1 .

[0073] The CHBC output voltage is the overall output voltage of n H-bridge commutation units inside each phase CHBC.

[0074] Phase compensation method:

[0075] Taking phase A as an example, according to the Park transformation formula, if the phase angle of the primary voltage of the A-phase parallel transformer is As the rotation angle of the inverse Park transformation, the reference value U of the d-axis component of the CHBC output voltage is rd1 and the reference value U of the q-axis component rq1The reference value U of the A-phase CHBC output voltage obtained by inverse Park transformation r1_a for:

[0076]

[0077] Park change formula:

[0078]

[0079] Inverse Park transformation formula:

[0080]

[0081] It can be seen that the reference value of the A phase CHBC output voltage U r1_a The primary voltage U of the transformer connected in parallel with phase A E1a There is a phase deviation. Therefore, it is necessary to compensate the rotation angle θ of the inverse Park transform, that is, phase compensation. The following is the calculation process of the compensation phase:

[0082] Assume that the reference values ​​of the d-axis and q-axis components of the overall output voltage and current of the n H-bridge commutation units in the A-phase CHBC are (U rd1 , U rq1 ,I cd ,I cq ) After the inverse Park transformation, the A-phase voltage and current of CHBC are:

[0083]

[0084] Where, δ and α are the phase differences of the overall output voltage and current of the n cascaded H-bridge converter units in the A-phase CHBC relative to the primary side voltage and current of the A-phase parallel transformer, respectively. is the amplitude of the reference value of the overall output voltage of n H-bridge commutation units inside CHBC; It is the reference value of the overall output current of the n H-bridge converter units inside CHBC.

[0085] according to Figure 4 The single-phase equivalent circuit of the controllable phase shifter HPFC and the single-phase equivalent circuit of CHBC shown in the figure are based on the primary side voltage U of the A-phase parallel transformer. E1a The phase is the reference phase, that is, the primary side voltage U of the A-phase parallel transformer is set E1a The phase is 0 phase, and the reference value of the A phase CHBC output voltage can be obtained Contains equivalent resistance voltage and filter inductor voltage:

[0086]

[0087] Among them, R is the CHBC equivalent resistance, L is the filter inductance, ω is the angular frequency, and j is the imaginary unit. From the above formula, it can be seen that if the reference value of the A-phase CHBC output voltage is to be The phase of the A-phase parallel transformer primary voltage U E1a The phases are consistent, then the reference value of the A phase CHBC output voltage needs to be The imaginary part of is 0.

[0088] The solution is:

[0089]

[0090]

[0091] Therefore, the reference value of the A-phase CHBC output voltage should be The phase of the A-phase parallel transformer primary voltage U E1a Phase consistency requires that the reference values ​​of the d-axis and q-axis components of the overall output voltage of the n H-bridge commutation units within the A-phase CHBC (U rd1 , U rq1 ) The phase of the A-phase CHBC output voltage obtained after the inverse Park transformation is δ, so the following compensated θ can be used as the rotation angle of the inverse Park transformation:

[0092]

[0093] At this time, the reference value U of the overall output voltage of the n cascaded H-bridge commutation units inside the A phase CHBC is r1_a for:

[0094]

[0095] The reference value of the overall output voltage of n cascaded H-bridge commutation units in each phase CHBC is used as the modulation wave, and finally the three-phase modulation wave I can be obtained: U r1_a , U r1_b and U r1_c .

[0096] S4: Based on the average value of the CHBC phase capacitor voltage and the average value of the CHBC overall capacitor voltage, a three-phase modulation wave II is obtained by using a phase-to-phase voltage balancing control method.

[0097] Phase-to-phase voltage balancing control calculates the difference between the average value of the CHBC phase capacitor voltage and the average value of the three-phase CHBC overall capacitor voltage, and obtains the difference between the current of each phase and the d-axis component of the CHBC output current through the proportional link K2, and then obtains the compensation voltage amplitude of each phase through the proportional link K1, and finally multiplies it with the corresponding sinusoidal function to obtain the three-phase modulation wave II. The control model is:

[0098]

[0099] Where U r2_a The modulation wave 2 output by the controller to balance the average value of the capacitor voltage of phase A, U r2_b The modulation wave 2 output by the controller to balance the average value of the capacitor voltage of phase B, U r2_c is the modulation wave 2 output by the controller to balance the average value of the capacitor voltage of phase C, K1 and K2 are proportional coefficients; U dcave is the average voltage of the CHBC overall capacitance, U dcave_a , U dcave_b , U dcave_c are the average voltages of the CHBC phase capacitors of phases A, B, and C respectively; I cd is the d-axis component of the CHBC output current.

[0100] S5: Based on the capacitor voltages in the CHBC phase and the average value of the capacitor voltage in the CHBC phase, a three-phase modulation wave III is obtained by using an intra-phase voltage balancing control method.

[0101] In-phase voltage balancing control, the difference between the average voltage of each phase CHBC capacitor and the voltage of each capacitor in the phase is calculated, and the compensation voltage amplitude of each phase CHBC used to compensate for pulse delay is obtained through the proportional link K3. Finally, it is multiplied with the q-axis component of the CHBC output current of each phase and the corresponding cosine function to obtain the three-phase modulation wave III. The control model is:

[0102]

[0103] in, is the modulation wave output by the controller for balancing the capacitor voltage of the xth H-bridge commutation unit in phase A. is the modulation wave output by the controller to balance the capacitor voltage of the xth H-bridge commutation unit in phase B. is the modulation wave output by the controller for balancing the capacitor voltage of the xth H-bridge commutation unit in phase C, K3 is the proportional coefficient, are the capacitor voltages inside the A, B, and C three-phase CHBCs, and I cq is the q-axis current of CHBC, U dc_ave_a , U dc_ave_b , U dc_ave_c They are the average values ​​of the three-phase phase capacitor voltages. After the phases are stable, the average value of the CHBC phase capacitor voltages of each phase is the overall capacitor average voltage U dcave .

[0104] S6: Superimpose three-phase modulation wave I, three-phase modulation wave II and three-phase modulation wave III and use bipolar carrier phase-shift PWM technology to convert the superimposed modulation wave into a CHBC internal switch tube signal to control the output voltage amplitude and phase of the H-bridge commutation unit.

[0105] The three-phase modulation wave I (U r1_a , U r1_b and U r1_c )、Three-phase modulation wave Ⅱ (U r2_a , U r2_b and U r2_c ) and three-phase modulation wave III (U r3_a , U r3_b and U r3_c ) to perform superposition operation and obtain the superposition modulation wave (U r_a , U r_b and U r_c ); A PWM controller is used to compare the superimposed modulation wave with the carrier signal generated by the PWM controller through the bipolar carrier phase-shift PWM technology to obtain the on / off signal of the CHBC internal switch tube, thereby controlling the output voltage of the CHBC internal H-bridge commutation unit and finally obtaining the CHBC compensation voltage.

[0106] The CHBC compensation voltage is combined with the secondary side adjustable voltage to generate a phase-shift voltage with adjustable phase and amplitude. Through circuit connection, the phase-shift voltage is compensated to the primary side of the series transformer and then compensated to the power grid line to realize the HPFC control method.

[0107] CHBC has three working states: compensation state, cut-out state and blocking state. In the compensation state, CHBC operates normally and is used to fine-tune the compensation voltage of the HPFC injection line; in the cut-out state, all IGBT switches inside CHBC are turned on, the internal capacitor is short-circuited, and CHBC is cut out and running; in the blocking state, all IGBT switches inside CHBC are turned off, and the freewheeling diode charges the capacitor.

[0108] Assume that HPFC is installed in a 220kV line and the above method is used for power flow regulation. Figure 5 This is a simulation circuit diagram of an embodiment, in which the series transformer is a three-winding transformer, adopts a Y / D connection method, and the secondary winding ratio is 1:1; the parallel transformer adopts a Y / Y connection method, the turns ratio is 220:40, the secondary side tap switch is divided into 8 levels, and the step voltage of each level is 5kV; when the cascaded H-bridge converter is not put into use, the phase shift angle range is ±10.53°, and the carrier frequency is 1kHz. Figure 6 is the active power curve flowing through the HPFC, Figure 7 is the CHBC output voltage curve, Figure 8 is the CHBC output current curve, Fig. 9 is the average voltage curve of each phase capacitor inside CHBC. Figure 6 It can be seen that after adopting this control method, after CHBC is put into use, the line power can be gradually adjusted to the set line power reference value; Figure 7 ,8 It can be seen that when the power is adjusted after the CHBC is put into operation, the voltage and current output by the CHBC are gradually adjusted by the PWM controller until the line power and capacitor voltage are consistent with the reference value; Fig. 9 It can be seen that when power regulation is performed after CHBC is put into operation, the average value of the capacitor voltage of each phase inside CHBC gradually stabilizes to the capacitor voltage reference value.

[0109] The power target of the line connected with HPFC is set to 118MW, the capacitor voltage reference value is 0.8kV, the capacitor voltage reference value inside CHBC is 0.8kV, and considering the 5kV voltage difference of the tap changer on the secondary side of the parallel transformer, the number of cascaded H-bridge converters per phase in CHBC is set to 7 (7*0.8>5), the maximum output voltage amplitude is 5.6kV, and the three phases are 21. 4s ago, CHBC was in a locked state, and the system was working in a steady state. At 4s, CHBC regulated the line power. At 6s, CHBC basically completed the regulation of line power. The average voltage of each phase of CHBC was stable at about 0.8kV, and the line active power was stable at about 118kW.

[0110] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A control method for a controllable phase shifter based on power compensation and phase compensation, characterized in that: Includes steps: S1: Set the CHBC capacitor voltage reference value and line power reference value, and obtain the actual line power value and CHBC capacitor voltage; S2: Calculate the q-axis component reference value of the CHBC output current by using the power compensation control method based on the line power reference value and the line power actual value; Calculate the d-axis component reference value of the CHBC output current by using the overall voltage balancing control method based on the CHBC capacitor voltage reference value and the average value of the CHBC overall capacitor voltage; S3: Based on the q-axis component reference value of the CHBC output current and the d-axis component reference value of the CHBC output current, current control is used to obtain the reference values ​​of the d-axis and q-axis components of the CHBC output voltage respectively and phase compensation is performed to obtain a three-phase modulation wave I; S4: Based on the average value of the CHBC phase capacitor voltage and the average value of the CHBC overall capacitor voltage, a three-phase modulation wave II is obtained by using a phase voltage balancing control method; S5: Based on the voltage of each capacitor in the CHBC phase and the average value of the capacitor voltage in the CHBC phase, a three-phase modulation wave III is obtained by using an intra-phase voltage balancing control method; S6: Superimpose three-phase modulation wave I, three-phase modulation wave II and three-phase modulation wave III and use bipolar carrier phase-shift PWM technology to convert the superimposed modulation wave into a CHBC internal switch tube signal to control the output voltage amplitude and phase of the H-bridge commutation unit.

2. The control method of the controllable phase shifter based on power compensation and phase compensation according to claim 1, characterized in that: The power compensation control method in step S2 is: Calculate the actual value of line power P line With the reference active power value P ref The difference is used as input to perform PI control calculation, and the output of the PI control calculation is used as the reference value I of the q-axis component of the CHBC output current. cq_ref ; The PI control calculation formula is: in, is the proportional adjustment coefficient of the q-axis PI control, is the integral adjustment coefficient of q-axis PI control, and S is the Laplace operator.

3. The control method of the controllable phase shifter based on power compensation and phase compensation according to claim 2, characterized in that: The overall voltage balance control method in step S2 is: calculating the average value U of the overall capacitor voltage of CHBC dc_ref , the CHBC capacitor voltage reference value U dc_ref The average value of the total capacitance voltage of CHBC is U dc_ave The total capacitance error is obtained by subtracting the total capacitance error, and the PI control calculation is performed with the total capacitance error as input. The output of the PI control calculation is used as the d-axis component reference value I of the CHBC output current. cd_ref .

4. The control method of the controllable phase shifter based on power compensation and phase compensation according to claim 3, characterized in that: The phase compensation method is as follows: taking the primary side voltage phase of the parallel transformer as a reference, obtaining a reference value calculation formula for the CHBC output voltage, obtaining a phase difference δ of the CHBC output voltage relative to the primary side voltage of the parallel transformer and a phase difference α of the CHBC output current relative to the primary side current of the parallel transformer according to the reference value calculation formula for the CHBC output voltage; calculating a compensation phase angle according to the phase difference δ and the phase difference α, using the compensation phase angle as a rotation angle to perform an inverse Park transformation on the reference values ​​of the d-axis and q-axis components of the CHBC output voltage, and obtaining a three-phase modulation wave I.

5. The control method of the controllable phase shifter based on power compensation and phase compensation according to claim 4, characterized in that: The reference value calculation formula of the CHBC output voltage is: in, is the reference value of CHBC output voltage, is the reference value of the CHBC output voltage, is the amplitude of the reference value of the CHBC output current, R is the CHBC equivalent resistance, L is the filter inductance, ω is the angular frequency, and j is the imaginary unit.

6. The control method of the controllable phase shifter based on power compensation and phase compensation according to claim 5, characterized in that: The compensation phase angle is: in, is the primary side voltage phase angle of the parallel transformer, U rd1 is the reference value of the d-axis component of the CHBC output voltage, U rq1 It is the reference value of the q-axis component of the CHBC output voltage.

7. The control method of the controllable phase shifter based on power compensation and phase compensation according to claim 6, characterized in that: The phase-to-phase voltage balancing control method is as follows: the difference between the average value of the CHBC phase capacitor voltage of each phase and the average value of the overall capacitor voltage of the three-phase CHBC is calculated, and the difference between the CHBC current of each phase and the d-axis component of the CHBC output current is obtained through the proportional link K2, and then the compensation voltage amplitude of each phase is obtained through the proportional link K1, and finally multiplied with the corresponding sinusoidal function to obtain the three-phase modulation wave II.

8. The control method of a controllable phase shifter based on power compensation and phase compensation according to any one of claims 3 to 7, characterized in that: The intra-phase voltage balancing control method is as follows: the difference between the average value of the phase capacitor voltage of each phase CHBC and the voltage of each capacitor in the phase is calculated, and the compensation voltage amplitude of each phase CHBC used to compensate for the pulse delay is obtained through the proportional link K3, and finally the q-axis component of the output current of each phase CHBC and the corresponding cosine function are multiplied to obtain the three-phase modulation wave III.

9. The control method of the controllable phase shifter based on power compensation and phase compensation according to claim 8, characterized in that: The method for obtaining the reference values ​​of the d-axis and q-axis components of the CHBC output voltage is as follows: the CHBC output current is subjected to park transformation with the primary side voltage phase of the excitation transformer as the rotation angular frequency to obtain the d-axis component I of the CHBC output current. cd and the q-axis component I cq ; The d-axis component I of the CHBC output current is cd and the d-axis component reference value I of the CHBC output current cd_ref As input, the q-axis component of the CHBC output current I cq and the q-axis component reference value I of the CHBC output current cq_ref As input, the d-axis component I of the CHBC overall output current is controlled by a feedforward decoupling control strategy. cd and the q-axis component I cq Feedforward decoupling is performed to obtain the reference value U of the d-axis component of the CHBC output voltage rd1 and the reference value U of the q-axis component rq1 .

10. The control method of the controllable phase shifter based on power compensation and phase compensation according to claim 9, characterized in that: The CHBC includes three working states, including a compensation state, a cut-out state and a locking state.

Images