RU2187872C1 - Hybrid passive power corrector and its control process - Google Patents

Abstract

FIELD: correcting passive components of instant power in single-phase circuits. SUBSTANCE: hybrid passive power corrector intended for both reactive-power and power distortion correction is composite structure assembled of reactive power corrector built around one matching transformer with center tap for reactive power corrector in the form of correcting rectifier loaded into inductive load in the form of smoothing storage choke and power distortion corrector built around single-phase voltage inverter with storage capacitor in dc circuit and matching choke at power input. Its control process is aimed at producing magnetic current of desired magnitude and waveform across power input as result of adding currents of reactive power corrector and power distortion corrector. Reactive power for controlling correcting rectifier diodes is regulated by triple turn-on of each diode during supply voltage period at moment of equal periodic reference voltages and control voltages, being nonlinear functions of two control actions affording independent proportional control of phase shift and magnitude of corrector current first harmonic. Provision is made for derating voltage inverter with respect to low-frequency component of power being corrected thereby dispensing with auxiliary circuits for storage capacitor charging. EFFECT: enlarged power control range, simplified design. 3 cl, 8 dwg

Description

 The invention relates to power electronics and is intended to compensate for the so-called passive components of instantaneous electrical power, that is, equally as reactive power and distortion power in single-phase AC networks.

 The idea and general principles of construction and control of hybrid static compensators are known in the form of a system of mutually complementary reactive power compensation (CRM) devices designed to eliminate the basic component of passive power, which has, compared to others, the lowest frequency of network and load interaction and distortion power compensation devices (KMI) ), contributing to bringing the network current formed by adding the current of the compensated load and the CRM current to a sinusoidal shape with an amplitude value, are equal the active component of the fundamental wave of the load current (see, e.g., Power Electronics: Handbook Lane with it - M .: Energoatomizdat, 1987, s.237-243; RF Patent No. 2,146,848....). The need to develop integrated compensation systems is explained by the limited functional capabilities of modern compensators, namely, the CRM bandwidth that is not wide enough to be used to compensate for distortion power, on the one hand, and the limited energy intensity of the KMI, which does not allow generating power during sufficiently long time intervals - on the other. As a prototype, a device is adopted in which the KRM functions are performed by a compensation converter according to a single-phase two-half-wave rectification circuit, made on two-operation valves operating on an inductive load in the form of a smoothing storage choke in the range of leading control angles close to α = -π / 2, and the functions KMI are assigned to a voltage inverter with a storage polar capacitor in the DC circuit and a matching choke at the network input (see, for example, Supronovich G. Improving the coefficient Power Factor of Converting Units: Translated from Polish - M .: Energoatomizdat, 1985, p. 133). Hereinafter, it is assumed that the mains voltage remains sinusoidal, the compensation converter operates at a perfectly smoothed load current, and the transformation coefficient of the power matching transformer is unity.

 The disadvantage of the prototype should be recognized a limited range of smooth regulation of reactive power, due to the fact that with the known method of phase control of the compensation rectifier, there is a simultaneous change in both parameters that determine the reactive power of the compensator, the current and the phase shift of its main harmonic relative to the voltage at the network input, which close to the short circuit of the rectifier, limits the range of a possible change in the angle α. A well-known solution aimed at expanding the control range, suggests that the inverter in the KMI can serve not only to compensate for the distortion power created by the higher harmonics of the current, but also the low-frequency (reactive) component of the passive power. However, studies have shown that this is possible only with limited phase load angles in the presence of special circuits for recharging the storage capacitor, which leads to additional distortion of the mains current in the form of an “undercompensation” current and complicates the device.

 The aim of the invention is to expand the range of regulation of reactive power at the network input of the hybrid compensator, which creates the conditions for power unloading of the inverter as part of the KMI and, therefore, simplifying its design by eliminating these additional charging circuits of the storage capacitor.

 For this, a constructive combination of KPM and KMI is proposed on the basis of one common matching transformer with the midpoint of the secondary half-windings, to which are connected two fully controlled KMI valves, shunted by reverse diodes and simultaneously two pairs of KPM valves, the latter being made in the form of two identical parallel connected relative to the windings transformer of valve sets, each of which is made according to a half-wave rectification scheme with a midpoint and contains rectified in its circuit th current accumulating-smoothing inductor.

 Known methods for controlling hybrid compensators are aimed at obtaining the required magnitude and shape of the instantaneous current at the network input by adding the currents of CRM and KMI, each of which is formed by the principle of automatic control according to the deviation from the reference current. The signal for setting the CRM current can be the total passive component of the current of the compensated load, which is obtained by subtracting from the total load current its useful part in the form of the active component of the first harmonic, which has the frequency and shape of the mains voltage. The valves of the compensation converter as part of the CRM are usually controlled by a pulse-phase method, for example, by tripping each valve three times during a period of mains voltage. The signal for setting the network current in the KMI control loop is the indicated useful component of the load current. Switching the KMI inverter valves occurs with a high frequency lying outside the frequency bandwidth of the CRM. Moreover, each switching on of the valve leads to a certain increase in the instantaneous current at the inverter input due to the partial discharge of the storage capacitor, and subsequent switching off leads to a decrease in current, which is accompanied by a recharge of the storage capacitor with a reactive current. Alternating the indicated intervals with a high frequency and adjusting their duration on the basis of relay or pulse-width modulation principles allows achieving the desired shape of the instantaneous current at the input of the hybrid compensator.

с постоянным значением угла управления α₂ = π при каждом втором включении на периоде сети и опережающим углом управления при каждом третьем включении, по модулю равным

при этом сигнал ошибки регулирования, образующийся в результате вычитания из сигнала задания тока КМИ тока сети, подавать на управляющий вход модулятора длительности включенного состояния вентилей инвертора напряжения в составе КМИ.In order to expand the control range with periodic changes in the current of the compensated load, it is proposed to control the valves of the compensation converter as part of the CRM using two control signals U _i , U _φ proportional to the active and reactive components of the main harmonic of the current of the CRM task, with a lagging relative to the beginning of the positive half wave of the mains voltage on the valve anode, the angle of control at each first switching on the network period

with a constant value of the control angle α ₂ = π for every second inclusion on the network period and an advanced control angle for every third inclusion, modulo equal

at the same time, the control error signal resulting from the subtraction of the network current KMI from the signal for setting the current KMI current is applied to the control input of the modulator of the on-time state of the voltage inverter valves in the KMI.

 In cases of non-periodic nature of the change in the load current, the proposed algorithm should be supplemented by the supply of unlocking pulses simultaneously for every two valves in different valve sets connected to one half-winding of the transformer when the signs of the instantaneous values of the reference current and current at the input of the KRM coincide or by supplying unlocking pulses to the valves, connected to different transformer semi-windings when the signs of the specified coordinates do not coincide, alternating the work of a parallel-connected valve set s in rectifier and inverter modes from one half-cycle of the mains voltage to another.

 The essence of the proposed solution is independent parametric regulation within any necessary limits of the magnitude and phase of the compensator current as a function of the corresponding load parameters, creating conditions for two-way exchange of reactive power between the load and the compensator. In the event of a non-periodic change in the load current, the possible exchange of the reactive power of the compensator with the network can be prevented by briefly shunting the transformer input at intervals of mismatch of the sign of the instantaneous values of the reference current and the current of the compensator. These measures lead to the unloading of the KMI inverter from the low-frequency component of passive power, as a result, this device will work with a short-term alternation of the positive and negative signs of instantaneous power, without requiring additional recharging of the storage capacitor.

In FIG. 1 shows a schematic diagram of the power unit and a block diagram of the control circuits of the proposed device; figure 2 is a timing diagram illustrating the operation of the compensation Converter in the mode of CRM; in FIG. 3 - characteristics of a functional builder designed to convert parametric reactive power control signals U _i , U _φ into control signals U _y1 , U _y2 at the input of the SIFU of the compensation converter; in FIG. 4 is a timing diagram illustrating a method for controlling a hybrid compensator.

 The power circuit is made using a three-winding matching transformer 1, the primary winding of which is connected to the network in parallel with the compensated load. KRM is made on two valve sets connected in parallel with respect to the transformer windings, one of which contains two-operation valves 2, 3, and the other 4, 5. The load of these rectifiers is accumulative-smoothing chokes 6, 7, which are connected with the common point of the transformer to their midpoint and at the same time - with one of the poles of the polar storage transformer 8. The latter is part of the KMI, which is made in the form of a single-phase inverter on valves 9, 10, shunted by reverse diodes 11, 12, which means for magnetically linked inductors 13, 14 connect the transformer to the other pole of the storage capacitor.

Control circuits made according to the so-called of the minimum configuration, they contain a network current controller 15 and a parametric analyzer of the load current 16, the input terminals of which are connected to the voltage sensors of the network 17 and the load current 18. The signal for setting the network current i * _н1a in the KMI control circuit is compared using the comparison unit 19 with the feedback signal over the current of the network i * _c , forming a signal of regulation error Δi $\genfrac{}{}{0ex}{}{\text{*}}{\text{ki}}$ , which is input to the modulator 21 of the on-time state of the KMI valves. Received from the outputs of block 16, the signals of parametric control of reactive power U _i , U _{φ are} sent to the inputs of the functional builder 22, at the outputs of which, in accordance with the analytical dependencies (8) and (9), control signals U _y1 , U _{y2 are formed} , which enable the activation of the KRM valves with control angles α ₁ , α ₃ using a pulse-phase control system (SIFU) 23 with an output matching device 24. The purpose of the latter is to change the order of supply of control pulses to valves 2, 3 and 4, 5 with the aim of alternately transferring the valve sets to the rectifier and inverter mode on command of a signal coming from one of the outputs of the analyzer 16.

что дает возможность получить действующее значение основной гармоники этого тока и ее фазовый сдвиг

Записав выражение для средневыпрямленного тока компенсационного преобразователя

приходим к выводу, что реактивная составляющая основной гармоники тока на сетевом входе КРМ также зависит от произведения двух параметров

,
где a $\genfrac{}{}{0ex}{}{\text{*}}{\text{1}}$ =sinφ_к1 - фазовый параметр тока компенсатора;

относительный токовый параметр компенсатора.We obtain equations proving the possibility of parametric regulation of reactive power at the network input of the compensator. For this, the expression of the reactive component of the current of the compensated load can be represented as the product of two factors
I _н1р = I _н1 sinφ _y1 = U _i • U _φ , (1)
where U _i = I _n1 / I _n1max is the relative current parameter reduced to a certain maximum current I _n1max ;
U _φ = sinφ ₁ - phase load parameter. We show that the reactive component of the compensator current can be represented in a similar way. The diagrams in figure 2 show that when controlling with three turns of each valve of the CRM on the network period by a corresponding change in the control angles α ₁ , α ₃ , independent control can be achieved according to the desired law of the average rectified voltage U _d and current I _d - on the one hand and phase the shift of the fundamental current harmonic φ ₁ - on the other. Expanding the current curve of the compensator i _к (ν) in a trigonometric series, we write the expressions of the Fourier coefficients in the first term

which makes it possible to obtain the effective value of the fundamental harmonic of this current and its phase shift

Having written the expression for the average rectified current of the compensation converter

we conclude that the reactive component of the fundamental harmonic of the current at the RMS network input also depends on the product of two parameters

,
where a $\genfrac{}{}{0ex}{}{\text{*}}{\text{1}}$ = sinφ _k1 - phase parameter of the compensator current;

relative current parameter of the compensator.

Аналогично отыскивается модульное значение опережающего угла управления при третьем включении вентиля на периоде сети
|α₃| = arccosU_y2, (9)
где

Получаемые в соответствии с (8), (9) управляющие сигналы U_y1, U_y2 поступают на входы СИФУ (блок 23), которая согласно известному вертикальному принципу вырабатывает управляющие импульсы в моменты их равенства с опорными сигналами косинусоидальной формы (см. фиг.2). Рассчитанные по (8), (9) характеристики функционального построителя U_y1,2 = f(U_i, U_φ) приведены на фиг.3.The condition for complete compensation of the reactive power of the load implies the equality I _k1p = -I _n1p , which is achieved by equalizing the load parameters and the compensator a $\genfrac{}{}{0ex}{}{\text{*}}{\text{1}}$ = -U _φ , b $\genfrac{}{}{0ex}{}{\text{*}}{\text{1}}$ = U _i , provided that I _n1max = 8U / π ² R _d . It is believed that the generation of parametric control signals U _i , U _φ in accordance with the indicated relations occurs at the outputs of block 16. Their further conversion is carried out using a functional builder 22, the characteristic of which is easily found if we rewrite equations (2), (3) in the following form
U _φ = sinα ₁ -sin | α ₃ |; (6)
U _i = cosα ₁ + cosα ₃ -1. (7)
This system of equations is compatible and its solution with respect to the control angle when the valve is first turned on during the network period gives
α ₁ = arccosU _y1 , (8)
Where

Similarly, the modular value of the leading control angle is found when the valve is turned on for the third time during the network period
| α ₃ | = arccosU _y2 , (9)
Where

Received in accordance with (8), (9), the control signals U _y1 , U _y2 are fed to the SIFU inputs (block 23), which, according to the known vertical principle, generates control pulses at the moments of their equality with the reference signals of a cosine shape (see Fig. 2 ) The characteristics of the functional builder U _y1,2 = f (U _i , U _φ ) calculated according to (8), (9) are shown in Fig. 3.

The operation of the hybrid compensator is illustrated by the timing diagrams in FIG. 4. It is believed that the compensated load consumes a non-sinusoidal periodic current i _n , which can be used to isolate the active i _n1a and reactive i _n1p components. Subtracting the load of its useful part from the total load current, a signal for setting the current of the CRM is obtained (shown by the solid line in Fig. 4a). Analysis of these components leads to the appearance of control signals U _i , U _φ at the outputs of block 16, and signals U _y1 , U _y2 at the outputs of block 22 (Fig. 4b, c). Switching valves KRM with control angles α ₁ , α ₃ leads to the appearance on the network input current of the compensator i _to (Fig.4g). With a periodic form of the load current, there is no need for two parallel-connected valve sets, therefore, it is believed that in the universal circuit of Fig. 1, control pulses arrive only at the valves of one of the sets, for example, with a positive half-wave of the mains voltage - to valve 2, and with a negative half-wave - to valve 3.

The reactive component of the compensator current should be out of phase with the reactive component of the load current i _k1p + i _n1p = 0, which provides the proposed control method. However, in the general case, higher harmonics Δi _n = i _n - (i _н1а + i _н1р ) are present in the load current, and the active component Δi _к = i _к -i _к1р can also be present in the instantaneous current of the compensator (see fig.4d , e). The total value of these components forms the network undercompensation current Δi _c = Δi _n + Δi _k (Fig. 4g), which can be obtained at the output of node 19 as a control error signal in the KMI control loop Δi $\genfrac{}{}{0ex}{}{\text{*}}{\text{ki}}$ = -Δi $\genfrac{}{}{0ex}{}{\text{*}}{\text{c}}$ . The processing of this signal, as noted, involves high-frequency switching using block 21, depending on the polarity of the signal Δi $\genfrac{}{}{0ex}{}{\text{*}}{\text{ki}}$ , valve 9 or 10. So, for example, switching on 9 will lead to a partial discharge of the storage capacitor along the circuit with elements 8, 13, 9 and, accordingly, to a certain increase in current in the transformer winding, and subsequent shutdown of this valve will lead to the closure of a decreasing reactive current along a circuit with elements 14, 8, 12 and a repeated charge of the capacitor 8. It is believed that the indicated ampere-current additions should lead to the compensation of the component Δi _c , as a result of which a current i _with the size and shape will flow in the network, which is close to the reference signal i * _n1a (figs).

The achieved unloading of the KMI from the reactive component of the current is manifested in the fact that the undercompensation current Δi _c (the current of the KMI) has the form of pulses of alternating polarity. The short duration of these pulses at intervals of the negative sign of instantaneous power (the sign of the instantaneous power of the KMI is indicated in Fig. 4g) helps to maintain a constant voltage across the plates of the storage capacitor, which is a condition for the operability of the KMI. At the same time, the presence of the active component in the current of undercompensation can cause an unacceptable decrease in the level of the indicated voltage, which especially complicates the operation of the KMI in case of violations of the periodicity of the load current.

For additional power unloading of KMI in the specified conditions, it is proposed to perform the KPM in the form of two valve sets in parallel. This allows you to briefly disconnect the CRM from the network input at intervals of mismatch of the signs of the instantaneous current of the reference and the current of the compensator while maintaining the rectified current in the circuits of the storage chokes, which will also contribute to the circulation of the low-frequency component of power between the compensator and the network. For this, it is sufficient to simultaneously turn on two gates connected to different half-windings of the transformer, which are part of different sets, for example, valves 2 and 5. As a result of the countercurrent flow of currents through the secondary half-windings of the transformer, the resulting current value in the network winding at the indicated interval will be zero. Since one of the valve sets will be switched to inverter mode at this time, its current in the accumulating choke will decrease. To prevent this phenomenon, it is proposed that the specified shunting of the transformer windings be carried out in the process of alternating operation of valve sets in rectifier and inverter modes from one half-cycle of the network to another. The operation of the hybrid compensator with this control algorithm is illustrated by the diagrams in figure 5. In contrast to the data considered, these curves reflect the processes when the phase load parameter changes at the moment ν ₁ , and the current diagram of the compensator i _k at the transformer bypass intervals is shown by a dashed line.

Claims (3)

 1. A hybrid passive power compensator, the power circuit of which contains a reactive power compensator (CRM), containing a matching single-phase three-winding transformer, to the secondary semi-windings of which a set of two-operation valves with an accumulative-smoothing inductor in the DC circuit is connected, as well as a distortion power compensator (KMI) according to the scheme of a single-phase inverter on two-operation valves, shunted by reverse diodes connected by one terminal to the corresponding secondary half-windings of the announcing transformer, and the other terminals to one of the terminals of the polar storage capacitor, the second terminal of which is connected to the midpoint of the secondary half-windings of the transformer and the control circuit, made in the form of an automatic control system, the main elements of which are a network current setting device with voltage sensors connected to the input mains and load current, node for comparing the reference signal with the feedback signal for the current of the network, the system of pulse-phase control of two-operation valves KPM and a KMI valve on-time modulator, switching said valves, the control error signal generated by the comparison node being input to the specified modulator, characterized by introducing into the KPM a second identical set of two-operation valves with a storage-smoothing inductor in the DC circuit, and also two magnetically coupled chokes for operation in AC circuits, while valve kits are connected in parallel with the network inputs but, as dvuhoperatsionnye KMI valves connected to the respective secondary transformer poluobmotkam magnetically through said inductors. 2. A method for controlling a hybrid passive power compensator according to claim 1, by pulse-phase control of two-stage KRM valves based on a synchronous-vertical principle with three times switching on each valve during the network period and independent control of the rectified voltage and current values - on the one hand and the phase value the shift of the main harmonic of the current at the network input - on the other hand, by high-frequency control of the switching moments of two-stage KMI valves based on pulse-width or Relay modulation method, characterized in that the control dvuhoperatsionnymi valves ASO by means of two signals U _i, U _φ, proportional, respectively, active and reactive components of the fundamental wave of ASO reference current lagging with respect to the positive half-wave of the mains voltage at the anode of the control angle for each first turn on the valve during the network period

with a constant value of the control angle α = π for every second switch-on on the network period and a leading control angle for every third switch-on, equal to

wherein the control error signal resulting from the subtraction of the network current from the KMI current signal is fed to the control input of the modulator of the on-state duration of the two-operation KMI valves.  3. The control method according to claim 2, characterized by the supply of unlocking pulses simultaneously for every two valves as part of different valve sets connected to one half-winding of the transformer when the signs of the instantaneous values of the reference current and the current at the network input of the CRM coincide and the supply of unlocking pulses to the valves connected to different transformer semi-windings when the signs of the indicated currents do not coincide, alternating the operation of parallel-connected valve sets in rectifier and inverter modes from one half-cycle of networks th voltage to another.

Images