Patent Description:
Thyristor starters have been developed for starting synchronous machines such as generators and motors (for example, see <CIT> (PTL <NUM>)). A thyristor starter includes a converter that converts AC power into DC power, a DC reactor that smoothes DC power, and an inverter that converts DC power applied from the converter through the DC reactor into AC power with a variable frequency to supply the AC power to a synchronous machine. The AC power supplied to the synchronous machine is controlled whereby the synchronous machine in a stop state can be started and driven at a predetermined rotation speed.

"<NPL> discloses thyristor starters for starting synchronous machine, e.g. valve motor, with different control structures. Further, <CIT> discloses a control system for a power converter driving a synchronous motor, wherein a phase angle controller is responsive to the detected rotary position of the motor and determines the firing phase angle of the inverter. The related prior art is also disclosed in <CIT>, which relates to adjustable frequency machine-commutated inverted-synchronous AC motor drives.

In the thyristor starter described above, the inverter has at least six thyristors. The inverter can supply three-phase AC power to the synchronous machine to increase the rotation speed of the synchronous machine, by firing six thyristors two by two in order in synchronization with rotation of the synchronous machine.

However, when a short-circuit failure occurs in any of six thyristors during commutation operation of the inverter, another sound thyristor is fired, whereby a path is formed through which fault current flows through this thyristor. Consequently, components such as sound thyristors and armature windings are damaged by fault current. The larger the fault current is, the greater the damage on the components is, and the possibility that the components are damaged becomes higher.

The present invention has been made in order to solve the problem above, and an object of the present invention is to provide a thyristor starter capable of suppressing damage by fault current.

According to an aspect of the present invention, a thyristor starter that starts a synchronous machine includes a converter, a DC reactor, an inverter, and a controller. The converter converts AC power into DC power. The DC reactor smoothes the DC power. The inverter converts the DC power applied from the converter through the DC reactor into AC power with a variable frequency and supplies the AC power to the synchronous machine. The controller controls a firing phase of the inverter. The thyristor starter accelerates the synchronous machine from a stop state to a predetermined rotation speed by sequentially performing a first mode of performing commutation of the inverter by intermittently setting DC output current of the converter to zero and a second mode of performing commutation of the inverter by induced voltage of the synchronous machine. During a first time period from start of performance of the second mode to arrival of the induced voltage at a first voltage value, a phase control angle of the inverter is changed such that a value thereof becomes larger as a rotation speed of the synchronous machine becomes higher.

The present invention can provide a thyristor starter capable of suppressing damage by fault current.

Embodiments of the present invention will be described in detail below with reference to the drawings. The same or corresponding parts are denoted by the same reference signs and a description thereof will not be repeated.

<FIG> is a circuit block diagram showing a configuration of a thyristor starter according to an embodiment of the present invention. Referring to <FIG>, a thyristor starter <NUM> according to the embodiment of the present invention starts a synchronous machine <NUM> by accelerating the stopped synchronous machine <NUM> to a predetermined rotation speed.

Synchronous machine <NUM> includes a stator having armature windings ATU, ATV, and ATW and a rotor having a field winding <NUM>. Synchronous machine <NUM> is coupled to, for example, a gas turbine of a thermal power plant and is rotatably driven by the gas turbine. In the following description, a predetermined rotation speed may be referred to as "rated rotation speed". For example, when the frequency of an AC power supply <NUM> is <NUM>, the rated rotation speed is set to <NUM> rpm.

Thyristor starter <NUM> is connected to the secondary side of a transformer TR. The primary side of transformer TR is connected to AC power supply <NUM>. Transformer TR converts three-phase AC voltage supplied from AC power supply <NUM> into three-phase AC voltage having a predetermined voltage value and applies the three-phase AC voltage to thyristor starter <NUM>.

Thyristor starter <NUM> includes a converter <NUM>, a DC reactor <NUM>, an inverter <NUM>, and an exciter <NUM>. Converter <NUM> is a three-phase full-wave rectifier including at least six thyristors and converts three-phase AC power from transformer TR into DC power with a variable voltage.

DC reactor <NUM> is connected between positive-side output terminal 1a of converter <NUM> and positive-side input terminal 2a of inverter <NUM>. DC reactor <NUM> smoothes DC output current Id from converter <NUM>. Negative-side output terminal 1b of converter <NUM> and negative-side input terminal 2b of inverter <NUM> are connected to each other. Another DC reactor <NUM> may be connected between negative-side output terminal 1b of converter <NUM> and negative-side input terminal 2b of inverter <NUM>.

Three output terminals 2c, 2d, and 2e of inverter <NUM> are connected to three armature windings ATU, ATV, and ATW, respectively, of synchronous machine <NUM>. Inverter <NUM> is a three-phase external-commutated inverter including at least six thyristors U, V, W, X, Y, and Z. Inverter <NUM> converts the DC power applied from converter <NUM> through DC reactor <NUM> into AC power with a variable frequency and supplies the AC power to synchronous machine <NUM>.

Exciter <NUM> supplies field current If to field winding <NUM> of synchronous machine <NUM>. When the AC power is supplied from inverter <NUM> to armature windings ATU, ATV, and ATW, with field current If being supplied to field winding <NUM>, rotation of synchronous machine <NUM> is accelerated.

Thyristor starter <NUM> further includes current transformers <NUM> and <NUM>, a voltage detector <NUM>, a position detector <NUM>, a current detector <NUM>, an inverter controller <NUM>, and a converter controller <NUM>.

Current transformer <NUM> detects three-phase AC current flowing from transformer TR to converter <NUM> and applies a signal indicating the detected value to current detector <NUM>. Current detector <NUM> calculates DC current Id output from converter <NUM>, based on a signal from current transformer <NUM>, and applies a signal indicating the calculated value to converter controller <NUM>. Specifically, current detector <NUM> has a full-wave rectifying diode rectifier and converts the detected three-phase AC current into DC current Id.

Current transformer <NUM> detects current flowing from inverter <NUM> to armature windings ATU, ATV, and ATW of synchronous machine <NUM> and applies a signal indicating the detected value to position detector <NUM>.

Voltage detector <NUM> detects instantaneous values of three-phase AC voltages Vu, Vv, and Vw supplied to synchronous machine <NUM> from inverter <NUM> and applies a signal indicating the detected values to position detector <NUM>. Specifically, voltage detector <NUM> detects two line voltages of line voltages of three-phase AC voltages in armature windings ATU, ATV, and ATW of synchronous machine <NUM> (in <FIG>, AC voltage Vu-v between the U phase and the V phase and AC voltage Vv-w between the V phase and the W phase). In this way, AC voltages of the U phase, the V phase, and the W phase can be obtained through calculation by detecting at least two line voltages of AC voltage Vu-v between the U phase and the V phase, AC voltage Vv-w between the V phase and the W phase, and AC voltage Vw-u between the W phase and the U phase. This conversion from line voltage to phase voltage is performed in voltage detector <NUM> or position detector <NUM>.

Position detector <NUM> detects the position of the rotor of synchronous machine <NUM> based on signals from current transformer <NUM> and voltage detector <NUM> and applies a signal indicating the detected value to inverter controller <NUM> and converter controller <NUM>.

Inverter controller <NUM> controls a firing phase of inverter <NUM> based on a signal from position detector <NUM>. Specifically, inverter controller <NUM> includes a control angle calculator <NUM> and a gate pulse generator <NUM>.

Control angle calculator <NUM> calculates a phase control angle (firing angle) γ based on the detected position of the rotor of synchronous machine <NUM> and applies the calculated phase control angle γ to gate pulse generator <NUM>. Specifically, when control angle calculator <NUM> calculates a rotation speed of synchronous machine <NUM> based on a signal from position detector <NUM>, control angle calculator <NUM> sets phase control angle γ based on the calculated rotation speed. Control angle calculator <NUM> may calculate the rotation speed of synchronous machine <NUM> based on a signal from voltage detector <NUM> instead of position detector <NUM>.

Gate pulse generator <NUM> generates a gate pulse (firing command) to be applied to the gates of the thyristors of inverter <NUM>, based on phase control angle γ received from control angle calculator <NUM>. Inverter controller <NUM> corresponds to an embodiment of "controller".

Converter controller <NUM> controls a firing phase of converter <NUM>, based on a signal from position detector <NUM> and a signal from current detector <NUM>. Specifically, converter controller <NUM> controls a firing phase of converter <NUM> such that DC current Id output from converter <NUM> matches current command value Id*.

Converter controller <NUM> includes a speed controller <NUM>, a current controller <NUM>, a control angle calculator <NUM>, and a gate pulse generator <NUM>. Speed controller <NUM> calculates the rotation speed of synchronous machine <NUM>, based on the detected position of the rotor of synchronous machine <NUM>. Speed controller <NUM> generates current command value Id*, which is a target value of DC current Id, based on the calculated rotation speed.

Current controller <NUM> calculates a deviation ΔId between current command value Id* and DC current Id and generates a voltage command value VDC1* based on the calculated deviation ΔId. Specifically, current controller <NUM> includes a proportional element (P), an integral element (I), and an adder. The proportional element multiplies deviation ΔId by a predetermined proportional gain for output to the adder, and the integral element integrates deviation ΔId by a predetermined integral gain for output to the adder. The adder adds the outputs from the proportional element and the integral element to generate voltage command value VDC1*. Voltage command value VDC1* corresponds to a control command that defines DC voltage VDC1 to be output by converter <NUM>.

Converter <NUM> performs control such that DC voltage VDC1 is greater than DC voltage VDC2 on the input terminal side of inverter <NUM> by the amount of voltage drop by DC reactor <NUM>. DC current Id is thus controlled.

Control angle calculator <NUM> calculates phase control angle α based on voltage command value VDC1* applied from current controller <NUM>. Control angle calculator <NUM> applies the calculated phase control angle α to gate pulse generator <NUM>.

Gate pulse generator <NUM> generates a gate pulse (firing command) to be applied to the gates of the thyristors of converter <NUM>, based on phase control angle α received from control angle calculator <NUM>. The switching of converter <NUM> is controlled in accordance with the gate pulse generated by gate pulse generator <NUM>, whereby DC current Id in accordance with current command value Id* is output from converter <NUM>.

Referring now to <FIG>, the basic operation of thyristor starter <NUM> will be described.

<FIG> is a time chart showing the basic operation of thyristor starter <NUM>. <FIG> shows the rotation speed of synchronous machine <NUM>, an effective value of induced voltage produced in synchronous machine <NUM>, DC current Id output from converter <NUM>, and field current If.

In thyristor starter <NUM>, commutation of the thyristors in inverter <NUM> is performed using the induced voltage produced in armature windings ATU, ATV, and ATW of synchronous machine <NUM>. Such commutation is called "load commutation".

However, when the rotation speed of synchronous machine <NUM> is low, that is, at startup or at a low speed of synchronous machine <NUM>, the induced voltage produced in armature windings ATU, ATV, and ATW is low and therefore commutation of the thyristors may fail. For this reason, when the rotation speed of synchronous machine <NUM> is low, "intermittent commutation" is employed in which commutation of inverter <NUM> is performed by intermittently setting DC output current Id of converter <NUM> to zero.

As shown in <FIG>, thyristor starter <NUM> sequentially switches and performs the intermittent commutation mode (first mode) and the load commutation mode (second mode) so that synchronous machine <NUM> is accelerated from a stop state to the rated rotation speed.

Specifically, at time t = <NUM>, synchronous machine <NUM> in a stop state is started, and then thyristor starter <NUM> performs the intermittent commutation mode. In the intermittent commutation mode, DC current Id exhibits a pulse waveform. The peak value of each pulse is usually set to a constant value (Id = I0). The peak value is set, for example, such that the integrated value of AC power supplied to synchronous machine <NUM> during the intermittent commutation mode satisfies the amount of electric power for accelerating synchronous machine <NUM> in a stop state to the switching rotation speed.

Then, when the rotation speed of synchronous machine <NUM> reaches about <NUM>% of the rated rotation speed, thyristor starter <NUM> switches from the intermittent commutation mode to the load commutation mode. In the following description, the rotation speed at which the intermittent commutation mode switches to the load commutation mode may be referred to as "switching rotation speed". In the example in <FIG>, the switching rotation speed is about <NUM>% of the rated rotation speed.

When synchronous machine <NUM> in a stop state is started at time t = <NUM>, exciter <NUM> supplies constant field current If to field winding <NUM> (If = If0). Constant field current If causes a constant field magnetic flux to be produced in the rotor. Synchronous machine <NUM> is accelerated in this state, and thus, the magnitude (effective value) of the induced voltage produced in synchronous machine <NUM> changes proportionally to the rotation speed of synchronous machine <NUM>.

When the effective value of the induced voltage produced in synchronous machine <NUM> arrives at a predetermined voltage VE2, exciter <NUM> decreases field current If supplied to field winding <NUM>. As a result, the effective value of the induced voltage is kept at constant voltage VE2 even when the rotation speed changes.

<FIG> is a circuit diagram showing the configuration and the operation of inverter <NUM> shown in <FIG>. Referring to <FIG>, thyristors U, V, and W have anodes connected together to positive-side input terminal 2a and cathodes connected to output terminals 2c, 2d, and 2e, respectively. Thyristors X, Y, and Z have anodes connected to output terminals 2c, 2d, and 2e, respectively, and cathodes connected together to negative-side input terminal 2b.

One of thyristors U, V, and W and one of thyristors X, Y, and Z are conducting in synchronous with three-phase AC voltages Vu, Vv, and Vw, whereby inverter <NUM> converts DC power supplied from converter <NUM> through DC reactor <NUM> into three-phase AC power with a variable frequency and a variable voltage and applies the converted AC power to the stator (armature windings ATU, ATV, and ATW) of synchronous machine <NUM>. This can increase the rotation speed of synchronous machine <NUM>.

For example, as shown in <FIG>, when thyristors U and Z are conducting, U-phase voltage Vu of synchronous machine <NUM> appears at input terminal 2a of inverter <NUM> through inductance Lu and thyristor U, and W-phase voltage Vw appears at input terminal 2b of inverter <NUM> through inductance Lw and thyristor Z. That is, AC voltage Vw-u between the W phase and the U phase of synchronous machine <NUM> appears as DC voltage VDC2 between input terminals 2a and 2b. Reactors Lu, Lv, and Lw represent inductances of armature windings ATU, ATV, and ATW, respectively, of synchronous machine <NUM>.

<FIG> is a time chart schematically showing an ideal commutation operation of inverter <NUM> in the load commutation mode. <FIG> shows three-phase AC voltages Vu, Vv, and Vw, conducting thyristors of six thyristors U, V, W, X, Y, and Z of inverter <NUM>, and DC voltage VDC2 appearing between input terminals 2a and 2b of inverter <NUM>.

In <FIG>, the point at which line voltages Vu-v, Vv-w, and Vw-u are <NUM> V is the reference point of phase control angle γ, and at the reference point, γ = <NUM>°. In the load commutation mode, a gate pulse is applied to the thyristors at a time ahead in phase by a desired angle γ from the reference point. For example, a gate pulse is applied to thyristor V during a period in which thyristor U is conducting, and then a gate pulse is applied to thyristor W during a period in which thyristor V is conducting. Similarly, a gate pulse is applied to thyristor X during a period in which thyristor Z is conducting, and then a gate pulse is applied to thyristor Y during a period in which thyristor X is conducting.

In response to transition of the conducting thyristor, line voltages Vu-v, Vv-w, and Vw-u of synchronous machine <NUM> sequentially appear as DC voltage VDC2 between input terminals 2a and 2b of inverter <NUM>. Inverter controller <NUM> fires six thyristors U, V, W, X, Y, and Z two by two in order in response to rotation of synchronous machine <NUM> to control the path of current flowing through synchronous machine <NUM>.

<FIG> is a diagram showing an example of the relation between the rotation speed of synchronous machine <NUM> shown in <FIG>, and effective value VE of the induced voltage produced in synchronous machine <NUM> and phase control angle γ.

Referring to <FIG>, during acceleration of synchronous machine <NUM> from the stop state to the switching rotation speed (about <NUM>% of the rated rotation speed), phase control angle γ is maintained at substantially zero. When the rotation speed of synchronous machine <NUM> arrives at the switching rotation speed and the intermittent commutation mode switches to the load commutation mode, phase control angle γ is set at γ1 (γ1 > <NUM>).

As shown in <FIG>, constant field current If is supplied to field winding <NUM> at this time, and thus, effective value VE of the induced voltage produced in synchronous machine <NUM> increases proportionally to the rotation speed of synchronous machine <NUM>. During a time period from start of performance of the load commutation mode to arrival of effective value VE of the induced voltage at VE2 (corresponding to a time period T1 in the figure), phase control angle γ is maintained at constant value γ1.

As shown in <FIG>, when effective value VE of the induced voltage arrives at VE2, field current If supplied to field winding <NUM> is decreased. Furthermore, during a time period from arrival of effective value VE of the induced voltage at VE2 to arrival of the rotation speed of synchronous machine <NUM> at the rated rotation speed (corresponding to a time period T2 in the figure), phase control angle γ is changed in accordance with the rotation speed. As a result, during time period T2, effective value VE of the induced voltage is kept at constant voltage VE2 even when the rotation speed changes.

Here, we discuss a case where a short-circuit failure occurs, in which the anode and the cathode are electrically short-circuited in any one of six thyristors U, V, W, X, Y, and Z of inverter <NUM> in the load commutation mode.

For example, in a case where a short-circuit failure occurs in thyristor U, when a gate pulse is applied to thyristor V to make thyristor V conducting, a path of fault current Ia is formed so as to include thyristors V and U as shown in <FIG>. Then, sound thyristor V and components such as armature windings may be damaged by fault current Ia. The larger fault current Ia is, the greater the damage on the components is, and it is more likely that the components are damaged.

The path of fault current Ia shown in <FIG> can be represented by an equivalent circuit diagram as shown in <FIG>. In the equivalent circuit diagram in <FIG>, the inductance of reactor L corresponds to the total value of inductances of armature windings ATU and ATV. AC power supply voltage corresponds to line voltage Vu-v of synchronous machine <NUM>. It is assumed that the resistance component of each of armature windings ATU, ATV, and ATW is negligibly small.

When thyristor V is conducting, fault current Ia flows in thyristor V through reactor L. When the effective value of line voltage Vu-V is V, line voltage Vu-v is written as Equation (<NUM>) below.

Fault current Ia is current lagging behind line voltage Vu-v by <NUM>° in phase. In the case of γ = π/<NUM>, fault current Ia is given by Equation (<NUM>) below, where L is the inductance of reactor L, and ω is the rotational angular velocity of synchronous machine <NUM>.

<FIG> is an operation waveform of line voltage Vu-v and fault current Ia when π/<NUM> ≤ γ < π. The current waveform shown by a broken line in <FIG> indicates fault current Ia when γ = π/<NUM>.

Fault current Ia is a symmetrical waveform with respect to θ = π. The circuit equation in the thyristor V conducting period γ ≤ θ ≤ π + γ is given by Equation (<NUM>) below.

Solving Equation (<NUM>) with θ = ωt = π - γ and given a condition Ia = <NUM> results in Equation (<NUM>) below. This current waveform is the same as the one obtained by removing the portion of π - γ ≤ θ ≤ π + γ from the current waveform of γ = π/<NUM> (broken line).

Ia is largest when θ = π, and the maximum value is obtained by Equation (<NUM>) below.

According to Equation (<NUM>), when line voltage Vu-v of synchronous machine <NUM> and the phase control angle γ are constant, fault current Ia is larger as rotational angular velocity ω of synchronous machine <NUM> is smaller (that is, as the rotation speed of synchronous machine <NUM> is lower). According to this, the magnitude of fault current Ia depends on the rotation speed of the synchronous machine at the timing when a short-circuit failure occurs in the thyristors of inverter <NUM>. That is, the lower the rotation speed at that timing is, the larger fault current Ia is.

The conducting time of fault current Ia is represented by the rotation period of synchronous machine <NUM> × 2γ/2π. Therefore, the conducting time is inversely proportional to the rotation speed of synchronous machine <NUM>. This indicates that the lower the rotation speed of synchronous machine <NUM> is, the longer the conducting time of fault current Ia is.

In this way, if a short-circuit failure occurs in any one of six thyristors U, V, W, X, Y, and Z of inverter <NUM> during the load commutation mode, fault current Ia flows through components of thyristor starter <NUM> and synchronous machine <NUM>. The magnitude of fault current Ia is larger as the rotation speed of synchronous machine <NUM> is lower. In addition, the conducting time of fault current Ia is longer as the rotation speed of synchronous machine <NUM> is lower.

According to the time chart in <FIG>, the timing when the rotation speed of synchronous machine <NUM> is lowest in the load commutation mode is the timing immediately after the intermittent commutation mode switches to the load commutation mode. As shown in <FIG>, during time period T1 from start of performance of the load commutation mode to arrival of effective value VE of the induced voltage produced in synchronous machine <NUM> at VE2, phase control angle γ is maintained at constant value γ1. Therefore, during this time period T1, the conducting time of fault current Ia is inversely proportional to the rotation speed of synchronous machine <NUM> and is longer as the rotation speed is lower. Thus, if a short-circuit failure occurs during time period T1, the conducting time of fault current Ia is longer, leading to great damage to the components.

Then, in thyristor starter <NUM> according to the embodiment, phase control angle γ during time period T1 is changed in accordance with the rotation speed of synchronous machine <NUM>.

Control of a firing phase of inverter <NUM> performed by thyristor starter <NUM> according to the embodiment will be described below with reference to <FIG>.

<FIG> is a diagram showing the relation between the rotation speed of synchronous machine <NUM>, and effective value VE of the induced voltage produced in synchronous machine <NUM> and phase control angle γ, in thyristor starter <NUM> according to the embodiment, and is compared with <FIG>. In <FIG>, phase control angle γ shown in <FIG> is indicated by an alternate long and short dash line. Effective value VE of the induced voltage of synchronous machine <NUM> shown in <FIG> is equal to that shown in <FIG>.

As shown in <FIG>, when the intermittent commutation mode switches to the load commutation mode, phase control angle γ is changed during time period T1 such that a value thereof is larger as the rotation speed of synchronous machine <NUM> is higher. In the example in <FIG>, phase control angle γ continuously changes within the range of γ2 ≤ γ ≤ γ1 in accordance with the rotation speed of synchronous machine <NUM>. However, phase control angle γ may discretely change in accordance with the rotation speed of synchronous machine <NUM>. For example, phase control angle γ may change in a stepwise manner within the above-described range.

According to <FIG>, the lower the rotation speed of synchronous machine <NUM> is, the smaller phase control angle γ is. Therefore, the conducting time of fault current Ia can be shorter as the rotation speed of synchronous machine <NUM> is lower. For example, if a short-circuit failure occurs at the timing immediately after switching to the load commutation mode is performed, the conducting time of fault current Ia is shortened by a factor of γ2/γ1.

Furthermore, by making phase control angle γ smaller, the magnitude of fault current Ia during time period T1 is also made smaller as compared with <FIG>. For example, at the timing immediately after switching to the load commutation mode is performed, the magnitude of fault current Ia is shortened by a factor of (<NUM> - cosγ2)/(<NUM> - cosγ1). According to this, even if the rotation speed of synchronous machine <NUM> is low at the timing when a short-circuit failure occurs, the damage on the components by fault current Ia can be reduced.

The data indicating the relation shown in <FIG> can be stored in a memory within thyristor starter <NUM>. By referring to the data, converter controller <NUM> can generate current command value Id* based on the calculated rotation speed of synchronous machine <NUM>. The data may be in table format or in function format.

As described above, in the thyristor starter according to the embodiment of the present invention, by suppressing the increase in induced voltage produced in synchronous machine <NUM> in the intermittent commutation mode, the fault current at the timing immediately after the intermittent commutation mode switches to the load commutation mode can be reduced. As a result, the damage on the components of the thyristor starter and the synchronous machine by the fault current can be suppressed.

In the foregoing embodiment, synchronous machine <NUM> is a generator rotatably driven by a gas turbine in a thermal power plant. However, the embodiment is not limited thereto and synchronous machine <NUM> may be a synchronous machine for use in general industrial fields. For example, synchronous machine <NUM> may be a synchronous machine for a cooling blower in a steel plant.

The embodiment disclosed herein is illustrative and not limited to the description above. The scope of the present invention is defined by the claims.

Claim 1:
A thyristor starter (<NUM>) that starts a synchronous machine, the thyristor starter comprising:
a converter (<NUM>) that converts AC power into DC power;
a DC reactor (<NUM>) that smoothes the DC power;
an inverter (<NUM>) that converts the DC power applied from the converter through the DC reactor into AC power with a variable frequency and supplies the AC power to the synchronous machine (<NUM>);
a detector (<NUM>, <NUM>) that detects AC current and AC voltage supplied to the synchronous machine (<NUM>) from the inverter (<NUM>);
a position detector (<NUM>) that detects a position of a rotor of the synchronous machine (<NUM>) based on a signal from the detector (<NUM>, <NUM>); and
a controller (<NUM>) that controls a firing phase of the inverter (<NUM>), wherein
the thyristor starter (<NUM>) accelerates the synchronous machine (<NUM>) from a stop state to a predetermined rotation speed by sequentially performing a first mode and a second mode, the thyristor starter (<NUM>) performing, in the first mode, commutation of the inverter (<NUM>) by intermittently setting DC output current (Id) of the converter to zero, the thyristor starter (<NUM>) performing, in the second mode, commutation of the inverter (<NUM>) by induced voltage of the synchronous machine (<NUM>), characterized in that
the controller (<NUM>) includes:
a control angle calculator (<NUM>) that calculates a rotation speed of the synchronous machine (<NUM>) based on a signal from the position detector (<NUM>) and calculates a firing angle (γ) of the inverter (<NUM>) based on the calculated rotation speed of the synchronous machine (<NUM>), and
a gate pulse generator (<NUM>) that generates a firing command to be applied to the inverter (<NUM>) based on the firing angle (γ) received from the control angle calculator (<NUM>), and
during a first time period (T1) from start of performance of the second mode to arrival of the induced voltage at a first voltage value (VE2), the firing angle (γ) of the inverter (<NUM>) is changed such that a value thereof becomes larger as the rotation speed of the synchronous machine (<NUM>) becomes higher.