System connection device for generated electrical energy

Abstract

System connection device for generated electrical energy for connecting an electrical energy system (7) to an output of an energy generator (1) by means of a connection inverter (5), wherein the device comprises the following: a magnetic energy regeneration circuit (2) comprising a bridge circuit per phase of the energy generator (1) constructed from four reverse-conducting semiconductor switches (SW1-SW4; SW5-SW8, SW9-SW10) and with a capacitor (Cu, Cv, Cw) for condensing magnetic energy condensed in the energy generator (1) which is connected between its DC terminals; a rectification circuit (3) connected to the magnetic energy regeneration circuit (2) for converting the electrical energy generated by the energy generator (1) and for outputting a converted current to the interconnection inverter (5); and a capacitor (4) connected to the output side of the rectification circuit (3) to maintain the output to the interconnecting inverter (5) at a predetermined voltage; A control circuit (10) for controlling the switching on and off of the bridge circuits of the magnetic energy regeneration circuit (2), wherein in the magnetic energy regeneration circuit (2) when a bridge circuit of one phase is switched off, the electrical energy stored in the leakage inductance of the phase of the energy generator (1) is delivered to the capacitor (Cu, Cv, Cw) of the bridge circuit, and when the bridge circuit of the phase is switched on, the energy stored in the capacitor of the bridge circuit is delivered to the capacitor (4) which is connected to the output side of the rectification circuit, wherein the control circuit (10) keeps a voltage held in the capacitor (4) constant by shifting the phase of an output voltage of the energy generator (1) from the switching operation.

Description

[0001] The present invention relates to a system connection device for generated electric power, which device is configured to connect an electric power system to an output side of a power generator via a connection inverter. More specifically, the present invention relates to the system connection device for generated electric power, which device does not suffer from an increase in the current capacity of a conversion device resulting from a deterioration in the power factor caused by a leakage inductance of a power generator.

[0002] Recently, wind energy, which utilizes inexhaustible and renewable energy, has become very prevalent worldwide as an environmentally friendly power generation system. In such wind energy generation systems, attention is currently focused on variable-speed technology, which works to significantly reduce the output fluctuation of a power generator.

[0003] In a case where a power generator is driven by a windmill to rotate by wind energy, and electric power generated by the wind power generator is regenerated in a commercial electric power system, it is necessary to reduce generation costs and improve generation reliability, and further obtain effective power based on efficient regeneration of electric power. This type of problem related to system interconnection is disclosed in Japanese Patent Laid-Open No. 2897208B2. Furthermore, reducing output fluctuation, reducing high-operation current, lowering noise, and improving maintainability are described in Isamu Nagata, et al.: "Development of Gearless Variable-speed Wind Turbine" (Technical Report of Mitsubishi Heavy Industry, Ltd., Vol. 38, No. 2, pp. 100-103, March 2001).

[0004] Fig. 4 is a circuit diagram showing a generation system that connects an electric power system to an output of a conventional power generator via a link inverter. This generation system is configured to include a generator 1 coupled to a rotating shaft of a propeller 100, a PWM rectifier 9 connected to the output side of the power generator 1 via a filter 8, a capacitor 4 and a PWM inverter 5, both of which are connected to the DC output side of the PWM rectifier 9, and a filter 6 connected between an output of the PWM inverter 5 and an electric power system 7. Here, each of the PWM rectifier 9 and the PWM inverter 5 is configured from a three-phase bridge circuit having six switches, each of which is formed from an IGBT and a diode connected in parallel with the reverse bias.

[0005] Fig. Figure 5 shows an arrangement of a converter used in the Fig. 4 shown power generation system, and the operating waveform of the converter. Fig. Figure 6 is a Feather view showing a relationship between a voltage vector and a current vector in the power generation system.

[0006] Fig. 5B shows the current and voltage waveforms that appear in the case of controlling an output voltage Vu of the PWM rectifier 9, to which an IGBT gate signal of the three-phase bridge circuit is supplied, so that an energy factor 1 can be derived from an armature voltage Vuint and an output current Iu of the energy generator 1. The Fig. The power generator 1 shown in FIG. 5A changes its terminal voltage according to the amplitude and phase of the current output from the power generator 1. Thus, in order to flow a current such that the voltage Vuint of each armature winding and the output current of the power generator 1 are mixed into a power factor of 1, it is necessary to output an output voltage Vu whose amplitude is greater than the armature voltage Vuint to the PWM inverter 5 by delaying the phase of the output voltage Vu.

[0007] In Fig. 6, the voltage Vx is a voltage generated by a leakage reactance X in the armature winding of the energy generator 1. The amplitude of this voltage is determined by a product of the leakage reactance X and the output current Lu of the energy generator.

[0008] Letting a control phase angle θ be, the output energy P0 of the energy generator 1 is represented by the following expressions (1) and (2): Po=3⋅Vu⋅Iu⋅cosθ P0=3⋅Vuint⋅Iu

[0009] Furthermore, the following applies: Cosθ=1 / 1+x2 where x denotes one percent of the impedance of the leakage reactance X.

[0010] Thus, since the capacity of the PWM rectifier 9 is 3 · Vu · Iu, for the electrical energy output by the energy generator 1, 1+x2−times as large as the one supplied in the case where the energy factor is 1. Thus, it is necessary for the capacity of the converter of the PWM inverter 5, 1+x2−times to be as large as that provided in the case where the energy factor is 1.

[0011] The PWM inverter 5 and the filter 6 control the output voltage in phase synchronization with the electrical power system 7, so that the electrical energy condensed in a capacitor 4 can be output to the electrical power system 7. At the same time, the PWM inverter 5 serves as a link converter for controlling the phase and voltage values ​​of the output voltage. As such, the PWM inverter 5 controls the magnitude of the electrical energy to be output to the electrical power system 7.

[0012] The conventional system connection device requires that the PWM rectifier 9 has a (1 + x 2 ) ½ -times as large a capacity. Thus, the PWM rectifier 9 is made larger in size. Furthermore, because the PWM rectifier 9 has the (1 + x 2 ) ½-times an output voltage Vu, the PWM rectifier 9 must be constructed of a highly durable semiconductor device. Therefore, a highly durable semiconductor device generally incurs greater conduction loss and switching loss than a less durable semiconductor. These energy losses pose a difficulty in effectively conserving energy.

[0013] Furthermore, because the PWM rectifier 9 attenuates harmonic components of a carrier frequency, a filter is required to be connected to the PWM rectifier 9. To reduce the size of the filter 8, a high-frequency filter of several kHz or more is generally used. Thus, the PWM rectifier 9 disadvantageously incurs larger switching loss and makes the system connection device larger in size and more expensive.

[0014] Further prior art is JP 2004 - 147 423 A. This describes an energy converter for converting AC energy into DC energy, wherein the AC energy is generated using a permanent magnet AC generator. It includes a converter consisting of six diodes connected in a three-phase bridge configuration, as well as an inverter for converting the energy supplied by the converter back into AC energy at a power grid frequency and for supplying the energy to the power grid.

[0015] Furthermore, JP 2004 - 260 991 A discloses another AC power supply device capable of improving the power factor of an AC load, in particular having a bidirectional current switch for regenerating magnetic energy inserted in series with an AC load instead of a conventional phase-advance capacitor.

[0016] In view of the above embodiments, a technical problem of the present invention is to provide a system connecting device for generated electric power with reduced dimensions but increased efficiency.

[0017] According to the present invention, this technical problem is solved by a system connection device having the features of claim 1.

[0018] The present invention is made in view of these aspects, and it is an object of the present invention to provide a system connection device for generated electric power, which device can be constructed in a smaller scale and more efficiently by incorporating a magnetic energy regeneration circuit.

[0019] In carrying out the object, a system connection device for generated electric power is provided for connecting an electric power system to the output side of a power generator through a connection inverter. This system connection device for generated electric power comprises: a magnetic energy regeneration circuit having a magnetic energy condensing capacitor for condensing magnetic energy condensed in the power generator; a rectification circuit connected to the magnetic energy regeneration circuit and for converting electric power generated by the power generator into a direct current (DC) and outputting the DC to the connection inverter; and a capacitor connected to the rectification circuit and for holding the DC output.DC output to the connecting inverter at a predetermined voltage.

[0020] The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

[0021] A brief description of the drawings follows: Fig. 1 is a circuit diagram showing a system connection device according to an embodiment of the present invention. Fig. Figure 2 shows in detail a magnetic energy regeneration circuit and its peripheral circuits. Fig. 3 shows a simulated result of current and voltage waveforms of the Fig. 1 shown system connection device. Fig. 4 is a circuit diagram showing an electricity generation system for connecting an electric power system to the output of the conventional power generator via a link inverter. Fig. 5A and Fig. 5B represent an arrangement of a device in the Fig. 4 and its operating waveform. Fig. 6 is a Feather view showing a relationship between a voltage vector and a current vector in the Fig. 4 shows the energy generator system.

[0022] The following is a description of the preferred embodiments.

[0023] Hereinafter, the embodiment of the present invention will be described with reference to the accompanying drawings. Fig. 1 is a circuit diagram showing a system connection device according to an embodiment of the present invention.

[0024] It is assumed that the system connection device used in Fig. 1, as the power generator 1, includes a synchronous generator that is directly driven by the rotation of a propeller 100. The output of the synchronous generator is connected to an electrical power system 7 via a PWM inverter 5, which serves as a connecting inverter. The difference between this system connecting device and the one shown in Fig. The device shown in Figure 4 is as follows. First, instead of the PWM rectifier 9, a diode rectifier 3 consisting of six diodes D1 to D6 is used. Second, a magnetic energy regeneration circuit 2 is arranged between the power generator 1 and the diode rectifier 3. The magnetic energy regeneration circuit 2 is formed of bridge circuits, each of which consists of four reverse-conducting semiconductor switches SW1 to SW12 and has a capacitor Cu, Cv, or Cw connected between its DC terminals. These bridge circuits correspond to the phase outputs of the power generator 1, respectively. Here, each of the reverse-conducting semiconductor switches SW1 to SW12 consists of an IGBT and a diode connected in parallel with the IGBT in reverse bias.A capacitor 4 for holding a DC output at a predetermined voltage, a PWM inverter 5, a filter 6, an electric power system 7, and the other components are identical to those shown in . Fig. 4. Thus, their description is omitted.

[0025] Fig. Figure 2 shows the magnetic energy regeneration circuit in detail.

[0026] The AC power generated in power generator 1 is extracted from each armature winding Xu, Xv, or Xw. The AC power from these three phases is supplied to the magnetic energy regeneration circuit 2. The regeneration circuit 2 includes three bridge circuits, each of which consists of three reverse-conducting semiconductor switches SW1 to SW4, SW5 to SW8, or SW9 to SW12, and a capacitor Cu, Cv, or Cw for condensing magnetic energy. The AC output of each bridge circuit is converted into a DC voltage by the diode rectifier 3, and then the AC voltage is held in the capacitor 4.

[0027] The magnetic energy regeneration circuit 2 is connected to a control circuit 10 for controlling each reverse-conducting semiconductor switch SW1 to SW12 by supplying a control signal to the gate of each switch SW1 to SW12. This control circuit 10 consists of a phase detector 11, pulse distributors 12, 13, and 14, and gate circuits 15, 16, and 17. Voltage phase signals sent from the armature windings Xu, Xc, and Xw are supplied to the phase detector 11. Then, the pulse distributors 12, 13, and 14 respectively generate PWM pulse signals according to the phase difference signals from these phases.In response to these PWM pulse signals, the gate circuits 15, 16, 17 output gate drive signals at the timing synchronized with the output voltage frequency of the power generator 1 in such a manner that a pair of reverse-conducting semiconductor switches arranged on a diagonal of each bridge circuit are simultaneously turned on and off.

[0028] In the following, the description will be directed to an on and off control of the regeneration circuit for magnetic energy 2.

[0029] First, the reverse-conducting semiconductor switches SW1, SW4, SW6, and SW7 are turned on so that the capacitor 4 can be charged with a DC voltage. At the same time, the reverse-conducting semiconductor switches SW2, SW3, SW5, and SW8 are turned off. In effect, current is supplied to the capacitor 4 in the passage from the V phase of the power generator 1 to the armature winding Xv to SW5 to SW6 to the diode D2 to the capacitor 4. Next, the same amount of current flows from the capacitor 4 itself in the passage from the diode D4 to SW4 to SW3 to the armature winding Xu to the U phase of the power generator.

[0030] Then, the reverse-conducting semiconductor switches SW1 and SW4 are turned off, allowing the magnetic energy condensed in the armature winding Xu to be shifted to the capacitor Cu. This means that the magnetic energy is transferred from the V-phase of the power generator 1 to the armature winding Xv to SW5 to SW6 to the diode D2 to the capacitor C4 to the diode D4 to SW2 to the capacitor Cu to SW3 to the armature winding Xu to the U-phase of the power generator 1.

[0031] When the polarity of the U-phase voltage of the power generator is reversed, the gate drive signals from the control circuit 10 are turned on at the timing synchronized with the reversal, so that the reverse-conducting semiconductor switches SW2, SW3, SW5, and SW8 are turned on. Then, the magnetic energy condensed in the capacitor Cu is shifted to the capacitor 4. This means that the current is caused to flow into the capacitor 4 by passing from the capacitor Cu to SW2 to the diode D1 to the capacitor 4, while the current is caused to flow out of the capacitor 4 by passing from the capacitor 4 to the diode D5 to SW6 to SW5 to the armature winding Xv to the V-phase of the power generator 1 to the U-phase of the power generator 1 to the armature winding Xu to SW1 to the capacitor Cu.As such, by applying a voltage corresponding to the magnetic energy condensed in the capacitor Cu, a large current is suddenly caused to flow into the capacitor 4. This results in an improvement in an energy factor.

[0032] As described above, in the magnetic energy regeneration circuit 2, when the bridge circuit is turned off, the magnetic energy condensed in the leakage reactance X of the power generator 1 is brought into the capacitor Cu, Cv, or Cw, and then, when the bridge circuit is turned on, the energy condensed in the capacitor is discharged into the capacitor 4 connected to the output side of the diode rectifier 3. The output current of the diode rectifier 3 suddenly increases when the bridge circuit is turned on. Thus, the current flowing through a load is caused to increase, causing a large amount of current to flow at a low voltage. This thus results in an improvement in the energy factor.

[0033] Furthermore, the magnetic energy regeneration circuit 2 only processes the energy capacity corresponding to the leakage reactance X. Thus, the diode rectifier 3, which serves as the AC / DC or direct current / alternating current converter, only needs to process the x (1 + x 2 ) -½ -times the capacity of the conventional PWM rectifier 9.

[0034] Furthermore, the magnetic energy regeneration circuit 2 only causes the reverse-conducting semiconductor switches SW1 to SW12 to be switched synchronously with the AC frequency of the power generator 1. This allows these switches SW1 to SW12 to be switched at a lower frequency than the conventional circuit. In this case, while maintaining a voltage in the capacitor 4, it is necessary for the control circuit 10 to control these reverse-conducting semiconductor switches SW1 to SW12 so that the pair of forward-current semiconductor switches and the pair of reverse-current semiconductor switches are not turned on simultaneously.

[0035] Similar to the phase control of the conventional PWM rectifier 9, by causing the reverse-conducting semiconductor switches SW1 to SW12 constituting the bridge circuits of the magnetic energy regeneration circuit 2 to be turned on and off when the switching operation is shifted from the phase of an output voltage of the power generator 1, it is possible to adjust a voltage value held in the capacitor 4. For example, in the case of controlling the U-phase voltage, by shifting the phase in which the reverse-conducting semiconductor switches SW1 and SW4 or the switches SW2 and SW3 are turned on from the phase of the armature voltage Vuint, like switching the phase of the conventional thyristor rectifier (PWM rectifier 9), it is possible to adjust the voltage value of the capacitor 4.

[0036] By further advancing the phase of a gate drive signal of the control circuit 10, the phase of the flowing current is caused to advance, while by delaying its phase, the current is caused to reduce. Furthermore, by delaying the phase by 180 degrees, the current is stopped. By turning off the reverse-conducting semiconductor switches SW1 to SW12, which form the bridge circuits of the magnetic energy regeneration circuit 2, the capacitors Cu, Cv, and Cw are charged to the peak voltage of the power generator 1, so that the electric power to be supplied to the capacitor 4 can be cut off. Therefore, this system connection device can use the magnetic energy regeneration circuit 2 to cut off the electric power system 7 or as a switch for synchronous turn-on.

[0037] Fig. 3 shows the simulated result of the operation of the system connection device. In Fig. 3, it is understood that for the system connection device equipped with the magnetic energy regeneration circuit 2, the current waveform at a switch has the same phase as the supply voltage waveform and, furthermore, has a larger current value. This indicates an improved energy factor of the load. Thus, this system connection device serves, in a broad sense, as an energy factor improving device.

[0038] The foregoing description has dealt with the embodiment in which the reverse-conducting semiconductor switch consists of a diode and an IGBT connected in parallel. In fact, however, a reverse-conducting GTO thyristor or a power MOSFET can be used for the reverse-conducting semiconductor switch. This switch provides the same effect.

[0039] As shown above, the system connecting device according to this embodiment can improve a power factor of the power generator 1 by using the magnetic energy regeneration circuit 2 having the corresponding capacitance with the leakage reactance X. Thus, this system connecting device can provide the converter that only uses the x (1 + x 2 ) -½-times the capacitance of the conventional PWM rectifier. This means that the wind power generation system can be reduced in size and manufactured more cheaply. Although the conventional PWM rectifier generally operates at several kHz, the system connection device according to the present invention can operate at the generator frequency of several tens of Hz. This makes it possible to reduce the switching loss by a factor of 1 / 100 or less. This reduction results in making the system connection device more efficient and smaller.

[0040] By controlling the on / off phase of the bridge circuit, it is possible to control the output voltage of the rectifier. Thus, this system connection device can operate without changing the output voltage even when the voltage of the power generator fluctuates. Thus, the PWM inverter 5, which corresponds to the load of the magnetic energy regeneration circuit 2, does not need to be larger to cope with a variety of input voltages, resulting in a reduction in the size of the device.

[0041] Furthermore, the magnetic energy regeneration circuit 2 can be used for disconnecting the power generator 1 from the electrical power system 7 or as a synchronous turn-on switch. The system connection device according to the present invention does not need to have mechanical switches, such as a conductor and a breaker for synchronous turn-on, which were required in the conventional system. This leads to a reduction in the size of the device. Furthermore, the magnetic energy regeneration circuit 2 enables faster turning on or off than the mechanical switches provided in the conventional system. This thus makes it possible to reduce the peak current or high-operation current that occurs during turning on.

[0042] According to the present invention, the magnetic energy regeneration circuit improves the energy factor of the power generator 1. This makes it possible to provide a system connection device for generated electrical power that can be made smaller and more efficient. Furthermore, the system connection device of this invention does not require mechanical switches, such as a conductor or a breaker for synchronous switching, which have been required in the conventional system.

Claims

[1] System connection device for generated electrical energy for connecting an electrical energy system (7) to an output of a power generator (1) through a connection inverter (5), the device comprising: a magnetic energy regeneration circuit (2) comprising a bridge circuit per phase of the energy generator (1) constructed from four reverse-conducting semiconductor switches (SW1-SW4; SW5-SW8, SW9-SW10) and with a capacitor (Cu, Cv, Cw) for condensing magnetic energy condensed in the energy generator (1) connected between its DC terminals; a rectification circuit (3) connected to the magnetic energy regeneration circuit (2) for converting the electrical energy generated by the energy generator (1) and outputting a converted current to the connection inverter (5); and a capacitor (4) connected to the output side of the rectification circuit (3) for maintaining the output to the connection inverter (5) at a predetermined voltage; a control circuit (10) for controlling the switching on and off of the bridge circuits of the magnetic energy regeneration circuit (2), wherein in the magnetic energy regeneration circuit (2), when a bridge circuit of a phase is turned off, the electrical energy stored in the leakage inductance of the phase of the power generator (1) is output to the capacitor (Cu, Cv, Cw) of the bridge circuit, and when the bridge circuit of the phase is turned on, the energy stored in the capacitor of the bridge circuit is output to the capacitor (4) connected to the output side of the rectification circuit, wherein the control circuit (10) keeps a voltage held in the capacitor (4) constant by shifting the phase of an output voltage of the power generator (1) from the switching operation. [2] The system connecting device according to claim 1, wherein the control circuit (10) generates a gate control signal for turning on or off a pair of the reverse conducting switches in a diagonal of the four switches each constituting a bridge circuit at a given time, for controlling the turning on or off of the magnetic energy regeneration circuit (2) by means of the gate control signal, and wherein the control circuit (10) controls in synchronism with the frequency of an output voltage of the power generator (1). [3] The system connection device according to claim 2, wherein the control circuit (10) controls a disconnection speed between the power generator (1) and the power system (7) or a synchronous turn-on speed. [4] The system connecting device according to claim 1, wherein the power generator (1) is a synchronous generator directly driven by rotation of a propeller (100). [5] The system connecting device according to claim 1, wherein the reverse conducting switch (SW1-SW12) is constructed of any parallel circuit of semiconductor switches each consisting of a power MOSFET, a parallel circuit of semiconductor switches each consisting of a reverse conducting GTO thyristor, and a parallel circuit of a diode and an IGBT.

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