CN102684204A - Cascading-type STATCOM DC side capacitor voltage balance control method - Google Patents

Abstract

The invention relates to a cascading-type STATCOM (Static Synchronous Compensator) DC (Direct Current) side capacitor voltage balance control method. In the control method, the direct current control and the indirect current control are combined. The method comprises the following steps: generating an active current reference value; selecting a special bridge; generating an STATCOM output current reference value; carrying out indirect current control of the special bridge; and carrying out direct current control of a non-special bridge. The control method provided by the invention is used for controlling the cascading-type STATCOM DC side capacitor voltage balance. The method not only ensures the balance of a DC capacitor voltage between H bridges and improves the response speed of a control link and optimizes the system performance, but also does not require an additional hardware circuit and cannot ensure the hardware cost of a STATCOM device to be increased.

Description

A cascaded STATCOM DC side capacitor voltage balance control method

technical field

The present invention relates to solving the control problem of cascaded static synchronous compensator STATCOM (Static Synchronous Compensator, referred to as STATCOM) DC side capacitor voltage balance control problem, specifically relates to a cascaded STATCOM DC side capacitor voltage balance control method.

Background technique

At present, STATCOM reactive power control is divided into two categories: direct current control and indirect current control. Direct current control, using tracking PWM control technology to perform feedback control on the instantaneous value of the current waveform, and directly control the generation of the command current. The indirect current control is to indirectly control the AC side current of the STATCOM by controlling the phase and amplitude of the fundamental wave of the AC voltage generated by the STATCOM inverter. Since the direct current control method is the tracking control of the instantaneous value of the current, the response speed of the control system is very fast when the switching frequency can meet the requirements. The indirect current control method does not have very high requirements on the switching frequency, and the large-capacity STATCOM is often used in combination with multiplexing, multi-level, PWM control and other technologies, but the response time is longer.

The cascaded H-bridge multi-level STATCOM is formed by cascading multiple voltage-type H-bridge inverters, and the DC side of each cascaded inverter unit is supported by capacitors. Since each DC side capacitor is relatively independent, if the output power of each unit is unbalanced or the loss and parameters of each unit are different, it will cause an unbalanced DC side capacitor voltage of each unit, which will cause STATCOM control performance to decline, and even cause DC side capacitors to be unbalanced. Overvoltage threatens the safe operation of the device.

In the cascaded multi-level STATCOM using phase-shifted carrier PWM, the balance control strategies of the capacitor voltage on the DC side mainly include two types of control with additional hardware circuits and without additional hardware circuits.

The methods of using additional hardware circuits include: adjusting the equivalent loss of the device by connecting an adjustable resistor in parallel with the DC side capacitor, based on the AC bus energy exchange method and using the DC bus energy exchange method, etc. Additional hardware circuits increase the complexity of the STATCOM circuit topology, increase the difficulty of control, reduce the reliability of the device, and increase the additional loss and cost of the device.

Strategies for controlling DC side capacitor voltage balance without using additional hardware circuits mainly include: DC side capacitor voltage individual control strategy based on power signal, DC capacitor voltage layered control strategy, and phase-separated instantaneous current tracking method to control capacitor voltage balance, refer to Literature [1]-[4].

[1] J.A.Barrena, L.Marroyo, M.A.Rodriguez, et al.DC Voltage Balancing for PWM Cascaded H-Bridge Converter Based STATCOM.IEEE IECON, Nov.7-10, 2006, Paris, France: 1840-1845.

[2] J.A.Barrena, L.Marroyo, M.A.Rodriguez. Individual Voltage Balancing Strategy for PWM Cascaded H-Bridge Converter-Based STATCOM. IEEE Transactions on Industrial Electronics, 2008, 55(1): 21-29.

[3] Zhao Ruibin, Qiu Yufeng, Jing Ping. A DC side voltage control method of cascaded STATCOM. Power Electronics, 2009 (4): 18-22.

[4] LIU Zhao, SHI Yan-jun, DUAN Shan-xu, et al. The Research of DC Capacitance Voltage Balancing Strategy Based on Cascade STATCOM Using Individual Phase Instantaneous CurrentTracking. IEEE ^6th International Power Electronics and Motion Control Conference-ECCE Asia. May 17-20, 2009, Wuhan, China: 1136-1140.

Contents of the invention

Aiming at the problems existing in the prior art, the object of the present invention is to provide a comprehensive current control method for cascaded multi-level STATCOM DC side capacitor voltage balance control. This method not only ensures the balance of the DC capacitor voltage among the H-bridges, improves the response speed of the control link, optimizes the system performance, but also does not require additional hardware circuits, and will not increase the hardware cost of the static synchronous compensator STATCOM device.

The object of the present invention is to adopt following technical scheme to realize:

A cascaded STATCOM DC side capacitor voltage balance control method, the improvement is that the control method includes the combination of direct current control and indirect current control;

The method comprises the steps of:

A. Generate active current reference value;

B. Select a special bridge;

C. Generate STATCOM output current reference value;

D. Special bridge indirect current control;

E. Non-special bridge direct current control.

A preferred technical solution provided by the present invention is: the direct current control includes feedback control of the instantaneous value of the current waveform to control the generation of the command current; the indirect current control refers to the AC voltage base generated by controlling the static synchronous compensator STATCOM The phase and amplitude of the wave indirectly control the AC side current of the static synchronous compensator STATCOM.

The second preferred technical solution provided by the present invention is: the active current reference value generation unit realizes the step A to generate the active current reference value; the active current reference value generation unit includes an adder I, a multiplier I, a subtractor I and Integrator I;

Described step A comprises the following steps:

A, make the input quantity of described active current reference value generation unit with N dc side capacitor voltage measurement value, be about to input the output quantity of measuring meter into adder I and sum, obtain sum value;

B, the sum value of described step a and constant quantity 1/N are used as the input quantity of multiplier I, and the output quantity of described multiplier I is the average value of N DC side capacitor voltages;

c. The average value and the DC side capacitor voltage reference value are input to the subtractor I, and the output of the subtracter I is the DC side capacitor voltage error value;

d. The DC side capacitor voltage error value is input to the integrator I for integration, and the result of the integration is the active current reference value.

The third preferred technical solution provided by the present invention is: the special bridge selection unit realizes the step B to select a special bridge; the special bridge selection unit includes N subtractors and a comparator 1;

Said step B comprises the following steps:

(1) With N DC side capacitance voltage measurement values and capacitance voltage reference values as the input quantities of the N subtractors, each of the DC side capacitance voltage measurement values and the capacitance voltage reference value are compared respectively to obtain N output quantities of N subtractors, where the N output quantities are N DC side capacitor voltage error quantities;

(2) The N DC side capacitor voltage error values are input into the comparator 1, and the DC side capacitor voltage error values are compared in pairs in the comparator 1 to obtain the maximum DC side capacitor voltage error value, and the maximum DC side capacitor voltage error value is obtained. The H-bridge of the DC side capacitor voltage error value is a special bridge.

The fourth preferred technical solution provided by the present invention is: the STATCOM output current reference value generation unit implements the step C to generate the STATCOM output current reference value; the STATCOM output current reference value generation unit includes a phase-locked loop, a sine function generator, cosine function generator, two multipliers, and adder II;

Described step C comprises the following steps:

i, with the measured value of the low-voltage side line voltage as the input of the STATCOM output current reference value generation unit, obtain the phase value of the low-voltage side line voltage measured value through the phase-locked loop;

ii. After the phase values are respectively input into the sine function generator and the cosine function generator, corresponding sine function values and cosine function values are respectively obtained;

iii. The sine function value and the active current reference value obtained in step A are used as the input of a multiplier; the cosine function value and the given reactive current reference value are used as the input of another multiplier to obtain two outputs quantity;

iv. Input the output of step iii into the adder II, the output value of the adder II is the STATCOM output current reference value.

The fifth preferred technical solution provided by the present invention is: the special bridge indirect current control unit realizes the step D special bridge indirect current control; the special bridge indirect current control unit includes two integrators, a multiplier II, and an adder III , subtractor II and PWM modulator I;

Said step D comprises the following steps:

①Using the maximum DC side capacitor voltage error value obtained in step B as the input of an integrator, the amplitude of the special bridge voltage correction value is obtained through the integration link, and the amplitude of the special bridge voltage correction value is the same as the output of step ii in step C Input the value of the sine function into the multiplier II together to obtain the voltage correction value of the special bridge;

② Superimpose the STATCOM output current reference value and output current measurement value obtained in step C in the subtractor II and then input it into another integrator for integration to obtain the special bridge voltage reference value;

③ Input the special bridge voltage correction value obtained in step ① and the special bridge voltage reference value obtained in step ② into the adder III, the output signal is used as the input quantity of the PWM modulator, and the pulse sequence is output, and the pulse sequence is used as the special bridge Pulse trigger signal for medium power switching devices.

The sixth preferred technical solution provided by the present invention is: the non-special bridge direct current control unit realizes the step E non-special bridge direct current control; the non-special bridge direct current control unit includes a subtractor III, two integrators and PWM Modulator II;

Described step E comprises:

The STATCOM output current reference value obtained in step C and the non-special bridge output current measurement value are superimposed in the subtractor III and then input into the two integrators in turn, and the output signal is used as the input quantity of the PWM modulator II, and the output pulse sequence is used as Pulse trigger signal for power switching devices in all non-special bridges except special bridges.

The seventh preferred technical solution provided by the present invention is: the method divides N cascaded H-bridge units into special bridges and non-special bridges.

A preferred technical solution provided by the present invention is: the special bridge refers to an H bridge controlled by an indirect current control method; the non-special bridge refers to an H bridge controlled by a direct current control method.

Compared with prior art, the beneficial effect that the present invention reaches is:

1. The STATCOM DC side capacitor voltage balance control method provided by the present invention introduces the concept of comprehensive current control, and combines direct current control and indirect current control methods to reduce the difficulty of control and improve the reliability of control.

2. The STATCOM DC side capacitor voltage balance control method provided by the present invention introduces the concepts of special bridges and non-special bridges, and sets different constraints according to actual requirements to select special bridges.

3. The STATCOM DC capacitor voltage balance control method provided by the present invention adopts indirect current control and direct current control for special bridges and non-special bridges respectively, so as to ensure that the DC capacitor voltages are balanced among the H bridges.

4. The STATCOM DC side capacitor voltage balance control method provided by the present invention adopts a comprehensive current control method to ensure that the DC capacitor voltage is balanced between the H-bridges, and has a fast response speed, which optimizes the performance of the STATCOM device.

5. The STATCOM DC side capacitor voltage balance control method provided by the present invention adopts comprehensive current control, does not require additional hardware circuits, does not increase the hardware cost of the STATCOM device, and simplifies the topology of the STATCOM circuit.

6. The STATCOM DC side capacitor voltage balance control method provided by the present invention has clear thinking and easy control.

Description of drawings

Fig. 1 is the flowchart of the STATCOM DC side capacitor voltage balance control method provided by the present invention;

Figure 2 is a single-phase cascaded H-bridge multi-level STATCOM topology diagram;

Fig. 3 is a topological structure diagram of an H-bridge unit;

Fig. 4 is the schematic diagram of the STATCOM DC side capacitor voltage balance control circuit provided by the present invention;

Fig. 5 is a structural diagram of the active current reference value generating link unit of the present invention;

Fig. 6 is a control block diagram of the active current reference value generating link of the present invention;

Fig. 7 is the structural diagram of the special bridge selection unit of the present invention;

Fig. 8 is a special bridge selection control block diagram of the present invention;

Fig. 9 is a structural diagram of the STATCOM output current reference value generating link unit of the present invention;

Fig. 10 is the control block diagram of the STATCOM output current reference value generating link of the present invention;

Fig. 11 is a structural diagram of the special bridge indirect current control unit of the present invention;

Fig. 12 is the control block diagram of the present invention adopting the indirect current control method to control the special bridge;

Fig. 13 is a structural diagram of a non-special bridge direct current control unit of the present invention;

Fig. 14 is the control block diagram of adopting direct current control method to control non-special bridge of the present invention;

Figure 15 is a waveform diagram of the capacitor voltage on the DC side of five H-bridge cascaded models.

Detailed ways

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

The STATCOM DC side capacitor voltage balance control method provided by the present invention is used to solve the control problem of cascaded static synchronous compensator (Static Synchronous Compensator, referred to as STATCOM) DC side capacitor voltage balance control problem, and can also be used to solve other cascade-based multi-voltage DC voltage balance control problem of power electronic equipment with flat inverter technology.

The H-bridge multilevel STATCOM includes three-phase six bridge arms, and each phase is a cascaded H-bridge. As shown in Figure 2, Figure 2 is a single-phase cascaded H-bridge multi-level STATCOM topology diagram, each phase cascaded H-bridge includes a high-voltage bus, a low-voltage bus, a single-phase transformer T, a reactor L, a resistor Rs, and N Cascaded H-bridge units, N DC side capacitors C ₁ -C _N and corresponding voltage measuring meters V ₁ -V _N , low voltage side line current measuring meters i _ab and low voltage side line voltage measuring meters u _AB .

The secondary side of the single-phase transformer T, the low-voltage side line voltage measuring meter u _AB , the reactor L, the resistance Rs, the low-voltage side line current measuring meter i _ab and N cascaded H-bridge units are connected in sequence; each H-bridge unit Connect in parallel with its corresponding measuring meter.

The topology structure of each H-bridge unit is shown in Figure 3, including 2 pairs of power switching devices P ₁ -P ₄ , 2 pairs of anti-parallel diodes D ₁ -D ₄ and 1 DC side capacitor.

Fig. 4 is a schematic diagram of the STATCOM DC side capacitor voltage balance control circuit provided by the present invention, the STATCOM DC side capacitor voltage balance control method provided by the present invention is realized by using a control circuit, and the control circuit includes sequentially connected active current reference value generating units 1. Generate a STATCOM output current reference value generation unit, a special bridge selection unit, a special bridge indirect current control unit and a non-special direct current control unit.

As shown in Figure 1, Fig. 1 is the flowchart of the STATCOM DC side capacitor voltage balance control method provided by the present invention, and the STATCOM DC side capacitor voltage balance control method provided by the present invention includes the following implementation steps:

1. Generate active current reference value.

Generating an active current reference value is realized by an active current reference value generating unit. As shown in Fig. 5, Fig. 5 is the structural diagram of active current reference value generation link unit of the present invention, and active current reference value generation unit comprises adder I, multiplier I, subtractor I and integrator I; Adder I, The multiplier I, the subtractor I and the integrator I are connected in sequence.

一起输入减法器，在减法器中得到的误差值输入积分器进行积分，所得结果为有功电流参考值 Take the output u _dc1 -u _dcN of the DC side measuring meters V ₁ -V _N as the input of the adder, that is, the N DC side capacitor voltage measurement values are input, and use the adder, multiplier, subtractor and integral implement. Put u _dc1 -u _dcN into the adder and sum to get the sum value; the sum value and the constant 1/N are used as the input of the multiplier, and the result is the average value of N DC side capacitor voltages; the average value is then combined with the given The capacitor voltage reference value of

Input the subtractor together, and the error value obtained in the subtractor is input into the integrator for integration, and the result is the active current reference value

为直流电容电压参考值，

为N个H桥电容电压平均值，u_dcj，为第j个H桥电容电压值，U_m为电网电压U_AB的幅值，

为有功电流参考值，T_f、k_u、τ_u为控制环节参数。将测量得到的N个H桥直流电容电压输入控制环节，求得平均值后与参考值比较得误差值。该误差值通过设计的控制环节后，得到有功电流参考值。由误差值得到有功电流参考值，也可通过其它控制策略实现，不仅限于图6虚线框中所示方案。As shown in Figure 6, Figure 6 is a control block diagram of the active current reference value generating link of the present invention, in which N H bridges are assumed to be cascaded,

is the reference value of DC capacitor voltage,

is the average value of N H-bridge capacitor voltages, u _dcj is the j-th H-bridge capacitor voltage value, U _m is the amplitude of grid voltage U _AB ,

is the active current reference value, T _f , k _u , τ _u are the parameters of the control link. The measured N H-bridge DC capacitor voltages are input into the control link, and the average value is obtained and compared with the reference value to obtain the error value. After the error value passes through the designed control link, the active current reference value is obtained. Obtaining the active current reference value from the error value can also be realized through other control strategies, not limited to the scheme shown in the dotted line box in Fig. 6 .

2. Special bridge selection.

The special bridge selection is realized by the special bridge selection unit. As shown in Figure 7, Fig. 7 is the structural diagram of the special bridge selection unit of the present invention, the special bridge selection unit comprises N subtractors and 1 multi-input comparator, and N subtractors and 1 multi-input comparator I are connected in series .

Same as generating the active current reference value, take the N DC side capacitor voltage measurement values u _dc1 -u _dcN as the input of N subtractors, and then input the capacitor voltage reference value to each subtractor The comparisons are performed respectively to obtain N voltage error quantities. These N voltage errors are input to the multi-input comparator of the next stage, and the maximum voltage error value Δu _dck is obtained by comparing them two by two. The subscript k indicates the number of the H-bridge with the maximum voltage error, which is a special bridge.

为直流电容电压参考值，u_dcj为第j个H桥电容电压值，Δu_dcj为第j个H桥电容电压值误差值。各电压误差值通过求绝对值环节abs后输入到求最大值环节max中，获得Δu_dck，即表明第k个H桥电容电压偏离参考值最多，需要对其进行电容电压修正。特殊桥的选择，不仅可以按照图8所示直流侧电容电压与其参考值误差的绝对值最大原则选取，也可将选择条件设定为误差绝对值最大的两个(或设定的其它数量)H桥、误差绝对值大于设定的门槛值的多个H桥、从正负两个方向误差值最大的两个(或设定的其它数量)H桥等。As shown in Figure 8, Figure 8 is a control block diagram for selecting a special bridge according to the principle of maximizing the absolute value of the DC side capacitor voltage and its reference value error. The number of H-bridges for control is relatively small, and non-special bridges dominate. In the figure,

is the DC capacitor voltage reference value, u _dcj is the jth H-bridge capacitor voltage value, Δu _dcj is the jth H-bridge capacitor voltage error value. Each voltage error value is input to the maximum value link max after going through the absolute value link abs, and Δu _dck is obtained, which means that the kth H-bridge capacitor voltage deviates the most from the reference value, and it needs to be corrected for the capacitor voltage. The selection of a special bridge can not only be selected according to the principle of the maximum absolute value of the error between the DC side capacitor voltage and its reference value shown in Figure 8, but also the selection condition can be set to the two with the largest absolute value of the error (or other set numbers). H bridges, multiple H bridges whose absolute error values are greater than a set threshold value, two (or other set) H bridges with the largest error values from positive and negative directions, etc.

3. Generate STATCOM output current reference value.

The generation of the STATCOM output current reference value is realized by the STATCOM output current reference value generating unit. As shown in Figure 9, the STATCOM output current reference value generation unit includes a phase-locked loop, a sine function generator, a cosine function generator, 2 multipliers and an adder II; a phase-locked loop, a function generator, a multiplier and an adder II is connected sequentially.

作为另外1个乘法器的输入，两个乘法器的输出得到的2个输出量再输入加法器中，加法器的输出得到和值，其和值就是STATCOM输出电流参考值

Taking the low-voltage side line voltage measurement value u _AB as the only input of the STATCOM output current reference value generation unit, the phase value θ of u _AB is obtained through the phase-locked loop. θ is input into the sine function generator and cosine function generator respectively, and the corresponding sine and cosine function values sinθ and cosθ are obtained. At this time, sinθ and the active current reference value obtained in step 1 As the input of 1 multiplier, cosθ and given reactive current reference value

As the input of another multiplier, the output of the two multipliers is input into the adder, and the output of the adder gets the sum value, and the sum value is the STATCOM output current reference value

为有功电流参考值，

为无功电流参考值，为STATCOM输出电流参考值。sinθ为与电网电压U_AB同相位的正弦分量。As shown in Figure 10, Figure 10 is a control block diagram of the STATCOM output current reference value generation link of the present invention, in the figure, U _AB is grid voltage,

is the active current reference value,

is the reactive current reference value, Output current reference value for STATCOM. sinθ is the sinusoidal component with the same phase as the grid voltage U _AB .

4. Special bridge indirect current control.

The special bridge indirect current control is realized by the special bridge indirect current control unit. As shown in Figure 11, Figure 11 is a structural diagram of the special bridge indirect current control unit of the present invention, the special bridge indirect current control unit PWM modulator I, adder III, subtractor II, multiplier IV, integrator II and integrator III; the subtractor II is connected with the integrator III to form the branch of the subtractor II and the integrator III; the multiplier IV and the integrator II are connected to form the branch of the multiplier IV and the integrator II; the adder III is respectively Connect with subtractor II and integrator III branch and multiplier IV and integrator II branch; Described PWM modulator I is connected with adder III;

将电压参考值

和电压修正值在加法器中叠加，输出的信号作为PWM调制器的输入量，输出脉冲序列，所述脉冲序列作为特殊桥中功率开关器件的脉冲触发信号。Taking the maximum voltage error value Δu _dck obtained in step 2 as the input of an integrator, the amplitude u _abk of the voltage correction value of the kth H-bridge (that is, the special bridge) is obtained through the integration link, and u _abk is obtained with step 3 The intermediate output sinθ is input to the multiplier together, and then the voltage correction value of the special bridge is obtained. At the same time, the output current reference value obtained in step 3 and the output current measurement value i _ab are superimposed in the subtractor II and then input into another integrator for integration to obtain the special bridge voltage reference value

Set the voltage reference value to

The sum voltage correction value is superimposed in the adder, and the output signal is used as the input quantity of the PWM modulator, and the pulse sequence is output, and the pulse sequence is used as the pulse trigger signal of the power switching device in the special bridge.

为STATCOM输出电流参考值，i_ab为输出电流测量值，

是由控制策略生成的H桥输出电压参考值。生成的控制策略也可通过其它控制策略实现，不仅限于图12虚线框中所示方案。As shown in Fig. 12, Fig. 12 is a control block diagram of the present invention using an indirect current control method to control a special bridge. The capacitance voltage of the kth H-bridge (special bridge) is corrected by using an indirect current control method. In the figure,

is the STATCOM output current reference value, i _ab is the output current measurement value,

is the H-bridge output voltage reference generated by the control strategy. generate The control strategy of can also be realized by other control strategies, not limited to the solution shown in the dotted box in Fig. 12 .

为直流电容电压参考值，u_dck为第k个H桥电容电压值，Δu_dck为第k个H桥电容电压值误差值。Δu_dck经过如图中虚线框所示的PID控制环节后，得到电压修正量的幅值u_abk，在与sinθ相乘得到第k个H桥输出电压修正值。k₁-k₄、τ₁-τ₄是控制环节的参数。sinθ为与电网电压U_AB同相位的正弦分量，图10控制环节的中间输出量。生成u_abk的控制策略也可通过其它控制策略实现，不仅限于图12虚线框中所示方案。

is the DC capacitor voltage reference value, u _dck is the kth H-bridge capacitor voltage value, Δu _dck is the k-th H-bridge capacitor voltage error value. After Δu _dck passes through the PID control link shown in the dotted line box in the figure, the amplitude u _abk of the voltage correction value is obtained, which is multiplied by sinθ to obtain the output voltage correction value of the kth H-bridge. k ₁ -k ₄ , τ ₁ -τ ₄ are the parameters of the control link. sinθ is the sinusoidal component of the same phase as the grid voltage U _AB , the intermediate output of the control link in Figure 10. The control strategy for generating u _abk can also be realized by other control strategies, not limited to the solution shown in the dashed box in FIG. 12 .

与其修正值的叠加信号，作为PWM调制器的输入量，即可得到第k个H桥的触发脉冲。

The superimposed signal with its correction value is used as the input quantity of the PWM modulator, and the trigger pulse of the kth H-bridge can be obtained.

5. Non-special bridge direct current control.

The non-specific bridge direct current control is realized by the non-specific bridge direct current control unit. As shown in Figure 13, Figure 13 is a structural diagram of the non-special bridge direct current control unit of the present invention, the non-special bridge direct current control unit comprises a subtractor, 2 integrators and PWM modulator II; a subtractor, 2 integrators Connect with PWM modulator II in turn.

和输出电流测量值i_ab在加法器中叠加后依次输入2个积分器中，所得信号作为移相PWM调制器的输入量，最终输出一组脉冲序列，作为除第k个H桥之外的所有非特殊桥中功率开关器件的触发脉冲信号。Since the DC capacitance voltage error value of the non-special bridge is within an acceptable range, no voltage correction is required, and a faster control response speed can be obtained by adopting DC current control. The STATCOM output current reference value obtained in step 3

and the output current measurement value i _ab are superimposed in the adder and then input into two integrators in turn, the obtained signal is used as the input quantity of the phase-shifted PWM modulator, and finally outputs a group of pulse sequences as Trigger pulse signal for power switching devices in all non-special bridges.

与i_ab的误差值经过PI环节和超前滞后校正环节后，得到命令信号i_cmd。i_cmd与具有相位差的一组载波信号比较后，输出非特殊桥的触发脉冲

(j＝1，…，k-1，k+1，…，N)。图中虚线框内的控制环节亦可用其他控制策略实现。As shown in Fig. 14, Fig. 14 is a control block diagram of a non-special bridge controlled by a direct current control method of the present invention. After the special bridge is selected, other H bridges can be collectively referred to as non-special bridges. is the reference value of the STATCOM output current, that is, the output of the control link in Figure 12, i _ab is the measured value of the STATCOM output current, k _p and _ki are the parameters of the PI link, τ ₁ and τ ₂ are the parameters of the leading and lagging control links.

After the error value with i _ab passes through the PI link and the lead-lag correction link, the command signal i _cmd is obtained. After i _cmd is compared with a group of carrier signals with phase difference, the trigger pulse of non-special bridge is output

(j=1, . . . , k-1, k+1, . . . , N). The control link in the dotted line box in the figure can also be realized by other control strategies.

After adopting the above-mentioned control implementation scheme, it is verified on the actual calculation example with 5 cascaded H bridges. Fig. 15 shows the voltage waveforms of each H-bridge capacitor before and after putting into the capacitor voltage balance control circuit designed by the present invention. Put into capacitor voltage balance control at 0.45s, where the long line U _dc is the average value of capacitor voltage. It can be seen that when the capacitor voltage balance control is not used, the capacitor voltage of each unit differs greatly from the average value. Taking unit I as an example, the maximum deviation can reach about 220V, and it will increase over time; After the capacitance voltage balance control, the capacitance voltage curve of each unit almost coincides with the average value, and the maximum deviation does not exceed 5V.

The STATCOM DC side capacitor voltage balance control method provided by the present invention not only ensures the balance of the DC capacitor voltage among the H-bridges, improves the response speed of the control link, optimizes the system performance, and does not require additional hardware circuits, and will not increase the STATCOM device hardware cost.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims (9)

1. a tandem type STATCOM dc capacitor voltage balance control method is characterized in that, said control method comprises that Direct Current Control and indirect current control combine;

Said method comprises the steps:

A, generation active current reference value;

B, select special bridge;

C, generation STATCOM output current reference value;

D, the control of special bridge indirect current;

E, non-special bridge Direct Current Control.

2. STATCOM dc capacitor voltage balance control method as claimed in claim 1 is characterized in that said Direct Current Control comprises FEEDBACK CONTROL current waveform instantaneous value, the generation of control command electric current; Said indirect current control is meant phase place and the amplitude that produces the alternating voltage first-harmonic through control STATCOM STATCOM, controls the ac-side current of STATCOM STATCOM indirectly.

3. STATCOM dc capacitor voltage balance control method as claimed in claim 1 is characterized in that, active current reference value generation unit realizes that said steps A generates the active current reference value; Said active current reference value generation unit comprises adder I, multiplier I, subtracter I and integrator I;

Said steps A comprises the steps:

A, make the input variable of said active current reference value generation unit with N dc capacitor voltage measured value, the output variable that is about to the meter meter is input among the adder I sues for peace, and obtains and is worth;

B, said step a with value and constant amount 1/N input variable as multiplier I, the output variable of said multiplier I is the mean value of N dc capacitor voltage;

C, said mean value and dc capacitor voltage reference value are input to subtracter I, and the output variable of said subtracter I is the dc capacitor voltage error amount;

D, said dc capacitor voltage error amount are input to integrator I and carry out integration, and the result of integration gained is the active current reference value.

4. STATCOM dc capacitor voltage balance control method as claimed in claim 1 is characterized in that special bridge selected cell realizes that said step B selects special bridge; Said special bridge selected cell comprises N subtracter and comparator I;

Said step B comprises the steps:

(1) with N dc capacitor voltage measured value and capacitance voltage reference value input variable as a said N subtracter; Each said dc capacitor voltage measured value and said capacitance voltage reference value compare respectively; Obtain N output variable of N subtracter, a said N output variable is N the dc capacitor voltage margin of error;

(2) said N the dc capacitor voltage margin of error is input among the comparator I; The said dc capacitor voltage margin of error compares in comparator I in twos obtains maximum dc capacitor voltage error amount, and the H bridge of said maximum dc capacitor voltage error amount is special bridge.

5. STATCOM dc capacitor voltage balance control method as claimed in claim 1 is characterized in that, STATCOM output current reference value generation unit realizes that said step C generates STATCOM output current reference value; Said STATCOM output current reference value generation unit comprises phase-locked loop, SIN function maker, cosine function maker, two multipliers and adder II;

Said step C comprises the steps:

I, be the input variable of said STATCOM output current reference value generation unit, try to achieve the phase value of said low-pressure side line voltage measurement value through said phase-locked loop with low-pressure side line voltage measurement value;

Ii, said phase value obtain sine function and cosine function value respectively after importing SIN function maker and cosine function maker respectively;

The active current reference value that iii, said sine function and steps A are tried to achieve is as the input of a multiplier; Said cosine function value and given reactive current reference value obtain two output variables as the input of another multiplier;

Iv, the output variable of step I ii is input among the adder II, the output valve of said adder II is STATCOM output current reference value.

6. STATCOM dc capacitor voltage balance control method as claimed in claim 1 is characterized in that, special bridge indirect current control unit is realized the special bridge indirect current control of said step D; Said special bridge indirect current control unit comprises two integrators, multiplier II, adder III, subtracter II and PWM modulator I;

Said step D comprises the steps:

1. the maximum dc capacitor voltage error amount that obtains with step B is as the input variable of an integrator; Obtain special bridge voltage correction amplitude through integral element; Said special bridge voltage correction amplitude output variable sine function of step I i in step C is imported multiplier II, obtains special bridge voltage correction value;

2. another integrator carried out integration after the STATCOM output current reference value input and output current measurement value that step C is obtained superposeed in subtracter II, obtained special bridge voltage reference value;

3. the special bridge voltage reference value that 2. special bridge voltage correction value that 1. step is obtained and step obtain is input among the adder III; The signal of output is as the input variable of PWM modulator; Output pulse sequence, said pulse train is as the pulse triggering signal of device for power switching in the special bridge.

7. STATCOM dc capacitor voltage balance control method as claimed in claim 1 is characterized in that, the non-special bridge Direct Current Control of said step e is realized in non-special bridge Direct Current Control unit; Said non-special bridge Direct Current Control unit comprises subtracter III, two integrators and PWM modulator II;

Said step e comprises:

After superposeing in subtracter III, STATCOM output current reference value that step C is obtained and non-special bridge output current measured value import successively in two integrators; The signal of output is as the input variable of PWM modulator II; Output pulse sequence, said pulse train is as the pulse triggering signal of device for power switching in all the non-special bridges except that special bridge.

8. STATCOM dc capacitor voltage balance control method as claimed in claim 1 is characterized in that, said method is special bridge and non-special bridge with the H bridge dividing elements of N cascade.

9. STATCOM dc capacitor voltage balance control method as claimed in claim 8 is characterized in that, said special bridge is meant the H bridge that adopts the control of indirect current control method; Said non-special bridge is meant the H bridge that adopts the control of Direct Current Control method.

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